I just recently purchased a gtx 275 and have been running all of my favorite games on all high settings an anti aliasing. Now it is time for me to play with crysis. I thought i would overclock considering this is a very GPU intensive game.
To make it simple.
When i overclock using Evga Precision, or Riva Tuner ( Havent tried any others ).
I get in game and then my fps drops seriously bad.
Example. 200fps in tf2 non overclocked 34 fps overclocked... (yeah... that bad)
Example. 50-60fps in crysis, 5-10 fps overclocked.
I restore default clock and it goes back to normal.
Whats going on? I have been running ATI cards in the past if that may be of some use.
Maybe you overclock too high and the GPU overheats, even though it is stable at those frequencies, and it throttles down.
Also, maybe the power supply is not capable to run the card when it's overclocked, but it can handle it at default frequencies.
You might also check if the ATI drivers have been completely uninstalled. (use Driver Cleaner).
I've been playing around and i've discovered that when in rivatuner and any other driver overclock software. When i go in game it stays at the low power 3D setting, when not, it goes into the performance as it should.
I had the same issue playing Halo 2 with my GTS250. Ultimately i rolled back the GPU speed and determined i had pushed it a little too far. I was surprised because i was expecting the system to freeze rather than throttle down.
I have the exact same problem and I think I figured it out.
The PSU didn't supply enough amps on the the 12V rail so whenever an overclock required more power, it would require too much from the PSU which wouldn't supply enough so the video card would change to it's bios preset throttle speed until reset.
Gonna get a new PSU this week and I'm pretty sure it'll fix the problem.