I used this thread:
https://forums.macrumors.com/threads/1142028/
Personally, I'm running my GPU at 770/925 @1.00v (read the thread and you'll understand completely).
In some cases it does run hotter, other times it stays the same temps. When my GPU is not under a lot of stress (TF2 or the like) it hits about 80C. But when the GPU is under heavy load (say....BF3

) it usually goes up to 84C while it loads textures (which can take awhile) then it goes back to 79C. Not that hot actually.
Good luck!
Okay, so I finally got to test it, and here's what happened:
First off, I'm not playing from my MBP screen; instead, I have connected my 32" LCD HDTV 720p 60Hz via HDMI, running at 1280 x 768 as an extended display. Also, I have all of my settings at medium and any antialiasing options turned off.
I opened ATT and started using whatever default value was set in overclocking, which happened to be 200/794 at 1.000V. Outside in the park, I got about 30-35 FPS (never got to the tunnels, as the game always ended at the park, lol). I didn't record the temperature (not sure how), but it felt the same as I would normally use it (going over warm).
Next, I tried your settings of 770/925 at 1.000V. Again, since the game always ended at the park, I saw a jump to about 40-50 FPS. The MBP felt hotter than the prior test, but not enough to really feel any major differences on my finger.
So overall, I think I'm satisfied with the overclock, but I don't think it's good to keep the overclock on for long hours. If I got a notebook cooler (like this one:
http://www.amazon.com/Thermaltake-M...XXWO/ref=sr_1_1?ie=UTF8&qid=1317619662&sr=8-1), would it significantly help reduce the temperature?