Alrighty, So for my recommendation.
Quick Specs:CPU: Intel i7-950
Mobo: ASUS P6X58D-E
GPU: Zotac AMP! GTX 470 1280Mb
PSU: XFX Black Edition 750W
RAM: Corsair Dominator DDR3 1600 6Gb (2gb x 3)
CPU Cooler: Thermaltake Frio
OS: Win 7 64-bit Home Premium
HDD: Samsung Spinpoint F3 1TB
DVD Burner: ASUS 24X Sata dvd burner
Case: SilverStone Raven
Misc.: Rosewill 74-in-1 card reader
Cost: $1,553.78
Alright now for the details....
CPU: You said you were interested in performance most of all, and while the Phenom II is a very good processor, It is by no means top dog. The i7-950 (I would have preferred the 930 but it's sold out atm) is about twice as powerful as the Phenom II, and is the most economical high performance processor out at the moment.
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16819115211Review: http://www.bit-tech.net/hardware/cpus/2010/03/01/intel-core-i7-930-cpu-review/1
Motherboard:With the I7 processor you will need to use a motherboard with a LGA 1366 cpu socket. This motherboard has lots of features, lots of capabilities, and plenty of room to expand. It also performs excellently and is very reasonably priced for a LGA 1366 motherboard.
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16813131641Review: http://www.bit-tech.net/hardware/motherboards/2010/08/20/asus-p6x58d-e-review/1GPU:Choosing what gpu to use was a bit more difficult since there are quite a few more gpu's going to be coming out the door in the next month or so. Ultimately I picked the GTX 470, and the Zotac AMP! edition specifically. While AMD offers great gpu's in the form of the 5000 series, and now the 6000 series. They actually have been getting more expensive due to the high demand for them. While Nvidia's cards have actually been getting cheaper because of the bad press they initially received. The price difference is big enough that the 470 is one of the best deals around for a super high performance card. The Zotac AMP! edition has a pretty spiffy cooler on it, that is quite a bit better than the stock 470, The only downsides to this card is it takes up 3 slots and the cooler itself isn't the sturdyest thing in the world so just dont be throwing your card around and you will be fine.
There are certantly card that perform better than the 470, but in trying to meet the $1500 budget this was the best way to go.
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16814500167Zotac Review: http://www.bit-tech.net/hardware/graphics/2010/10/20/zotac-geforce-gtx-470-amp-edition/1Highend Card review: http://www.bit-tech.net/hardware/graphics/2010/11/09/nvidia-geforce-gtx-580-review/1PSU:I had a few PSU's in mind, but I decided I like this XFX psu the best, since It A: Looks awesome, B: Has a big fan, and C: Performs very well at a decent price.
at $130, the 750W XFX Black Edition...is great value for money. If you're in the market for a 700-799W PSU then it should be at the top of your shopping list.'
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16817207003RAM:I ended up picking the Corsair Dominator DDR3 6 GB (2gb x 3) with having a LGA 1366 system, you also have the option to use triple channel ram. This will give you a slight performance boost over dual-channel ram. With ram the bandwidth ends up being a lot more important the the Latency of the ram. But since RAM is relatively cheap these days, I picked a 1600 MHz ram with a relativly low latency. The ram also comes with a very good set of coolers, I have RAM very similar to this, just being DDR2. Corsair's ram is almost always very reliable and fast, with a good costumer support and a warranty for the ram as long as you own it. I have used them on all the computers I have built and always had great results.
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16820145224CPU Cooler: The Thermaltake Frio is one of the best performing CPU coolers out, on top of that, it has two fans each with their own speed controller, and has a solid mounting mechanism with a compatability to use it on any current modern CPU.
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16835106150Review: http://www.bit-tech.net/hardware/cooling/2010/07/14/thermaltake-frio-cpu-cooler-review/1OS:You need a 64-bit operating system to make use of all you ram, and win 7 is the best version of windows to come out so far. I went with home premium since I cant imagine you would need any of the features offered in the other versions, so this will do quite nicely. When you are building a new computer go with the OEM version of the operating system since that is made to be installed on a blank computer.
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16832116754HDD:The new solid-state drives are pretty awesome bits of kit, but they are quite a bit more expensive than a standard hard drive. This Samsung drive is one of the fastest on the market for its size and is quite reliable, not to mention inexpensive!
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16822152185
Review: http://www.bit-tech.net/hardware/storage/2008/12/09/samsung-spinpoint-f1-1tb/1DVD Burner:DVD burners any more are kinda hard to pick since all are inexpensive, and on the whole perform relativly similarly. ASUS makes pretty good dvd drives, I have one and it is quite a nice drive, and has a really fast write speed compared to most drives. Along with overwhelmingly positive reviews.
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16827135204
Case: Case choice is a very personal thing since most people have different tastes on what they find pleasing. This silverstone case in my opinion looks quite nice, but what I like about it most is what makes it different from all the other cases. The motherboard layout is unique to silverstone. All of the "rear" plugins are actually on the top underneath a cover. This makes it really easy to hookup and take down. Next the panels are insulated so it cuts down on the noise a bit. Last the case fans used are some of the best on the market they are 180mm, much bigger than the standard case fan, it also has three of them moving air around the case. The case is kinda big, but for your first build you might like this a lot. The motherboard tray is removable making it a lot easier to do most of the initial component placement. The build quality is outstanding so its likely this case will last you for a couple of builds into the future.
Newegg Link: http://www.newegg.com/Product/Product.aspx?Item=N82E16811163154Review: http://www.bit-tech.net/hardware/cases/2010/09/09/silverstone-raven-rv02-review/1Misc:You had a card reader on your list so I assumed you wanted one, the one you picked out looks fine to me.
Newegg link: http://www.newegg.com/Product/Product.aspx?Item=N82E16820223109
In Summary:So now, the computer I picked out for you should perform over 2-3 times as well as that alienware you picked out. It will also do significantly better than the computer you build on new egg as well. If you ever find yourself with more cash upgrading to a Crucial C300 SSD drive would give you a big performance boost, as well as upgrading your video card to a higher performing one would help alot too.
There is one other thing this computer should be able to do very very well. That is overclocking, all of the components should have significant headroom for a little bit of overclocking, and if done right could increase the computers performance as much as 50%. I wouldn't recommend overclocking your computer if you are not at least relatively confident in your abilities, since there is a good chance of messing up your hardware if you do it wrong. But if you ever feel the need for extra performance, this computer should overclock quite nicely.
So go read the reviews of each product, I put them there for a reason. They will give you some insight into the components I picked, Bit-tech has always been a very reliable computer hardware news site, I've been visiting it since 2004 and haven't been disappointed yet.
So I hope this was helpful, I did my best in picking everything out. Good luck building your computer! (If you have anymore questions feel free to ask them here I'd be happy to answer them to the best of my ability)