My X5650 runs only 4.1Ghz 1.3v (OCCT Linpack passed).
I think my motherboard is crap, not really a decent overclocker. LoL.
Intel Desktopboard DX58OG only provides too few options to tweak with, compared to, for example, Asus P6T bios.
Rampage series, even 2nd hand, still too much for my wallet.