So I just recently bought the Gigabyte GV-N66TWF2-2GD in upgrade to my current MSI N460GTX Hawk. I bought the Gigabyte GTX660 because I heard that MSI was cheating in their factory overclocks, using abnormally high voltages to obtain their overclock. Apparently many were sent for repair. Although I really really liked My GTX460 Hawk, being disappointed by MSI, I bought the seemingly more stable Gigabyte instead. The factory overclocked version was out of stock, and the sales at my local computer store said they will not get anymore of it, so I bought the non-overclocked version: GV-N66TWF2-2GD. I was going to purchase online the overclocked version, but I thought, "what the hell", why waste 30 more bucks on 100 Mhz when I can just do it myself. So I've been trial-and-error-ing this card, trying to obtain the highest stable overclock. But it seems that I cannot go over 100Mhz, whereas on my GTX460 I could almost go to 200Mhz and be stable (during winter only, summer I have to tune down due to higher temps). But in the process of this, I forced on adaptive v-sync for the game i was testing, F1 2012. It crashed repeatedly, and that seemed to be the problem. I am just wondering, what are your highest overclocks with this card or similar cards?
If you have 100 Mhz OC, be happy. 941+100=1041 Mhz is already 9Mhz more than GV-N66TOC-2GD with 1032Mhz.
You could also try to OC memory to encrease its bandwidth. I set +331 Mhz to get 7332 Mhz and the bandwidth 176 GB/s (more than HD 7870 has with its bandwidth of 153.6 GB/s).
My GV-N66TI2WF@-2GD held GPU +110 MHZ and Memory +350 Mhz, but that was only in 3DMark11. In Far Cry 3 this pair of frequencies failed, and I lowered them down to +75/+331 and have played continuesly 5 hours without problem.
IMHO, I suspect that manufacturers select better chips for their factory-OCed cards, the chips that stand higher clocks. So, the factory-OCed chips are guaranteed to work at that higher clock, but as to non factory-OCed, it depends on your luck. Maybe also voltages differ.
Also bear in mind that these VGAs always work OC'ed in 3D applications. E.g., in my case, if I OC my card only +70Mhz (941+70), it actually works at ~1150 Mhz in Far Cry 3, which is +235 Mhz overclocking (915+235), and this is pretty much OK!
P.S. Actually, GV-N66TWF2-2GD is also factory OCed, not very much though. It even has the ad "OC Version" written on its retail box.