Hi everyone. I'm trying to figure out if I'm doing something wrong here, because I can't achieve any overclock on my graphics cards with stability. I have SLI GTX 470's in Nvidia surround, and I have the clocks and voltages synchronized between the cards. Even at the maximum voltage (1.087V), a 20MHz core overclock from 607MHz to 627MHz causes a system crash after about 5 minutes of OCCT. I am stress testing at surround resolution (5760x1200) to stress both cards, and GPU usage and temperatures confirm that both cards are being stressed simultaneously. What I'm trying to figure out is the reason for the inability to overclock and (if possible) how to solve it without spending more money. I have seen many reviews with water cooled GTX 470's reaching 750-800MHz, so I am suspicious of my failure to get any overclock. Temperatures are not an issue, as the cores never get above 50°C, and I think that my power supply is adequate for my system. I have two hypotheses: something with Nvidia surround prevents cards from operating above their stock frequencies, or one card is just completely unstable at anything above its stock speed, which seems unlikely. Maybe it's something different that I don't know. I appreciate suggestions. Thanks for the help in advance.