Try 400/1100 for a day and see how it performs. Run games like doom 3 if you have it or 3dmark2k5 to check for artifacts and temps under load. Check the idle temps of it when you are just surfing the web.
I tried for 400/1100 since that seemed to be the common number and had no problems with it. I monitored my temps idle, while surfing the web and under load with doom 3 for a few weeks to get the general idle and load temps. My temps were 48-51 idle and topped at 68 under load so i decided to try the 1.4 volt bios mod and now I run at 420/1100. Before the .1 volt increase, auto detect was 405/1100, after the .1 increase it is 418/1130 with idle temps from 50-54 and topped at 71 load. I didn't push the memory speed higher even though it detected higher after volt mod cause memory speed increases provided much smaller gains than increasing the core and cause 2D and 3D memorys is synchronized. Since 2D mode is set to 1.1 volt and 3D is 1.3 by default, raising the memory speed for 3D mode may have no problems at 1.4 but since i didn't increase the 2D mode volt, this might cause instability if i tried for higher memory speeds without increasing the 2D mode volt as well.
If you want to try the volt mod increase, it is done through a very simple bios flash to the videocard, there's no need to increase voltage to agp from the MB bios. But if you do decide to try .1 volt increase, check to make sure your idle temps under basic use is 55 or lower and that under load is 70 or lower. I only decided to do this cause my temps were only 48-51 idle and 68 load thus i had no worries of overheating. Most people that tried this had success in increasing or making their speeds more stable since the .1 increase is just bringing the GT to the Ultra standard of 1.4 volts.
