Framerate issues with g53-SW A1

Bought the notebook just over two years ago and it's mostly run fine except for a few audio/video driver glitches early on and of course the faulty Atheros wifi chip which I replaced (intel ultimate-n 6300 iirc). Anyway, over the last half a year the performance has considerably dropped in games that have all previously run completely fine. For example: Battlefield 3 which I could formerly run on high settings is now unplayable, even on low settings. I have the same issue in Skyrim, among other games; I'll play for about 3 minutes before the performance drops to ~5 fps (low settings, formerly ultra). I'm even now having issues with minecraft, even when the video settings are optimized for performance.

I can't really say when the performance drops first started happening or if it's just been a long-term performance decrease. I sometimes go 1-3 months without playing any games, depending on how busy I am in school. My initial idea was to do a fresh install of windows 7 and wipe my hard drive (both the os partition and alternate partition have +100 GB free space). However, I assume this sort of performance drop over time is common with pcs over 2 years old, so I figured I'd post here for ideas.