Exactly, just because the board uses LGA 775 doesnt mean it has to support 1333MHz FSB CPUs, or even 1066MHz FSB CPUs either. 775 started with only 800MHz CPUs and many cheap/prebuilt boards only support 800MHz, same happened when 1066MHz CPUs came later (yes, 1333MHz came further back than 1066MHz FSB so the same applies).
Then why even get a new CPU? I thought you're moving from a dual core to a quad core. In this case the performance gain won't be big, if you want more performance it's time for DDR3-only platforms like 2nd gen Core, 3rd gen Core (Sandy Bridge and Ivy Bridge) or on AMD's side Athlon x4 7/8xx, Axx-7xxx at least, maybe even the Phenom II x4/x6 (the CPUs before / during Bulldozer years that nearly killed AMD for good)
How about some other (cheaper) CPU model + an overclock? I've seen the 2.4GHz Q6600 go above 3,6 easily.
On the same architecture, a difference of 100-400 mhz per core isn't something an average user can distinguish.
Deano Langster reacted to Jurrunio in In Search of Core 2 Quad Q9705 3.16GHz
