Games on windows 8 in bootcamp lag even on lowest graphics

Everything starts fine, but gets progressiveness worse after about 10 minutes of play, and I left it go for an hour once, and it was REALLY bad. This is bizarre.

You pretty much nailed it down as a heat/throttling issue right here.

When performance drops off over time but isn't associated with a crash it's very commonly related to heat build-up in the system and the components throttling themselves to prevent overheating. Software possibilities were pretty much eliminated with the re-install you did.

It might be worth looking into cleaning the cooling fins if it's not been done recently. I don't know how easy or difficult the MBP is to work on but with other hardware I might even suggest re-applying the thermal paste with some high-quality material but how much difference that can make will depend entirely on how good the existing material is.

Have you installed direct x 9, 10 and 11 ? Try that. Did you install win 8 pro or just 8, I would try the other of what you have, you can find it on the internet, and if it works buy a upgrade. Your graph drivers are up to 310.61 in Beta, try that. Make sure you pick which bit, 32 or 64.

If you are a big gamer, 90 percent of games work better on win 7 then 8, Microsoft flight works better on 8.

You can try Furmark, and run a stability test and check your scores with other 650m.