Which cpu would you guys go with Intel Q9950 or AMD 6300 FX ? I'm going to put some old mother boards back in service for Prime Grid. Which would serve the Prime Grid cpu projects better overall.

That sort of depends on your situation, in general Intel cpu's crunch faster here at PG then AMD cpu's do,

The Q9550 is a true quad core. The FX6300 is a "Bulldozer" AMD CPU, and thus is substantially newer. It is also technically a 6-core processor, but this isn't quite true as the FX6300 has 6 integer cores, but only 3 float cores.

see here for a comparison.

So the answer depends on what you are going to run.

The FX6300 should be a good bit faster on sieve work. It also offers bigger cache and extra threads/cores that would be helpful to GPU processing in tandem with CPU usage (e.g., it would be better on the current WFS challenge on PRPnet). It also has a bit faster stock core clock.

That said, the Q9550 still has better single threaded performance (especially in floating point operations). For smaller to mid-sized LLR projects, that means it is probably a bit better overall than the FX6300 since it can run full tilt on 4 workunits at a time with LLR, whereas the FX6300 would be spreading LLR work across three float cores.

On larger LLR work, however, where FFT size is large and cache (and even physical RAM) is heavily used, the FX6300 has the advantage of an L3 cache, faster bus speed, and the potential to be used in a board with DDR3 memory, which should largely equalize the single thread performance issue.

If I were choosing, I would go with the FX6300 given its advantages in more numerous PG applications and for it being more "future-proof" since FFT sizes on all LLR projects are steadily increasing as we test further.