Maybe I am missing something, but I can get a 12 CORE mac pro for $5000, including everything but the screen the GPUs and some extra RAM (which is quite cheap if you don't buy official Mac RAM .
An 8 Core Mac pro is only $3500
How much would a 12 core PC be? Are they available? Are there even 8 core PCs available yet?
My 2008 Mac pro 8 core beats all PC performance reports I see here (without a Cubix expander). My 2009 8 core smokes these reports by a mile. It is so good that a Red Rocket is a luxury, not in any way an absolute need.
For 1080p work, my GTX 285 rarely looks unhappy even with gigantic node trees (the bottleneck is CPU Red Raw decoding, not the nodes) , and for a few hundred $$ I could upgrade later to a bigger/better GPU. (BTW - The Quadro 4000 is significantly slower - not sure why it is so expensive, but there are other cards you can get for the Mac - you just have to look around)
Again, maybe I am missing something....