Quad cores are still VERY new, and are changing monthly, so yeah it's a crapshoot.. and you won;t save a huge amount even using newegg for a power mac system.. you might shave $1000 off that system, but that still leaves you with a VERY expensive $900 system.. and you coul probably pick up 2 windows based quad core systems for that price, and network them as a render farm.

There WAS a thread somewhere here comparing render speeds of dual vs quad core poser rendering, but bear in mind poser is NOT supposed to be a high end pro app that uses the fastest and most optimised render engine available. It's supposed to be a prosumer entry into the 3d marketplace, and pro users pretty much scoff at using poser for anything useful at all.. check in any of the pro forums, or check the 3d job marketplace, and try to find anyone who even mentions poser

The pros pretty much consider poser as a low end consumer "toy".

Way too many people take way too many things way too seriously.