I've trying to pus my GTX 460 Hawks (SLI) recently but have found after about 810mHz during Heaven Demo the computer just freezes. Nothing pops up or crashes and I have to do a cold reboot. I thought it might be a PSU issue with only 750w but I saw an entry of someone pushing their CPU and GPUs on a 750w PSU. Is this really a problem of low power or can I fix it by upping the voltage on the cards?