Which Mac Pro for Logic Pro..?

I can't answer your specific question other than to say I'm running Logic 9 on a MBP, 2.66 i7, 8 GBs. I'm running 50+ tracks of virtual instruments, with a lot of FX. My samples are all installed on a separate drive, but I'm not even getting a hiccup with playback. Smooth as silk.

 

More processors are better.

 

Actually you'll get the best performance with the single CPU Mac Pro. Logic doesn't do a good job of multiprocessing. It's beats up one core for most tasks. There is supposedly a way to leverage other cores/cpu's by routing tracks through different buses or something to that effect, but that's a ridiculous solution. I'd really only recommend the multi cpu pro's for those using Final Cut Pro, Adobe After Effects or if you're doing a lot of encoding.

On a 2009 Mac Pro single quad, I've had 45+ tracks (combination of audio and virtual instruments) all with multiple plugins running and it doesn't even flinch.

 

3.33 ghz i7 6-core is better than a 2.4 ghz 8-core Mac Pro for Logic imo. You want each core to be fast too so none will hit their ceiling.

 

Alright, then.... more of the best processors, the better.