Notice how he never made the video.
As Deg said, he clearly doesn't understand that neither hard drive space OR RAM affect game performance. Your game performance is determined by two things: your GFX Card and your CPU.
I'd really love to see that video.
Well, HDD speed can cause lots of nasty stuttering in open world games like Skyrim or Fallout, where new parts are being loaded constantly.
Ram really only determines how many textures you can have loaded onto your buffer at one time and what resolution you can run them at.
And CPU really only affects the non-graphic related processes (NPC AI, particles, explosions, ect).
Yeah, it has absolutely nothing to do with his problem, and wouldn't affect his framerates or his mouse speed, just thought I'd point it out :x
Your bottleneck is most likely your CPU though. When you're in-game, your mouse is running independently from the game itself and is running on it's own instance on the processor. If you're getting bad framerates in-game, your mouse should respond instantly and have no latency issues. Some games lock the mouse to the game, so if you're getting low framerates or having stuttering issues because of your CPU, then that would explain it.
But that aside, I'd also like to see this video. Prove us all wrong.