Upgrading from a SATA II to a SATA III made my i7-920 unstable, I had to go from 4.2 GHz down to 3.8GHz. It was a pain in the ass to figure out because the error messages pointed to the video cards.
Was that a MB change or just switched a drive to a Sata3 port?
my i7-920 C0 wont clock as hight but thats due to other issues
like pushing a bit more juice for an extended time had it running around 4.1ghz 1.5vcore, 1.45qtt after that it didnt like more the 1.38v on either.., later had a waterblock plug up spiking temps over 95C for a few weeks, looked like it rebooted a few times due to overheating but as the system sets in a back room folding I didnt notice right away.... now it's setting happy at around 3.6ghz w/ ~1.34v pushing more volts just makes it unstable lol. I check on it a bit more often now still runs a bit warm (upper 70's) lol..