We've got a 2x2.93 xeon mac pro with 32 GB of ram, and a dual core AMD PC laptop with 8 gigs of RAM, Nvidia graphics both running CS6.
using MP, the laptop will render our admittedly heavy comp in under 3 minutes whereas the Mac Pro will take over 10 minutes to render the same thing.
This wasn't the case with CS5.5. The render times of the mac pro were considerably higher.
I've set the mac pro per Todd's recommendation at 3 CPUs for other apps, 3GB for background, and 8 GB RAM for other apps.
Any insight as to why the Mac Pro is so slow compared to a PC econobox?
You are likely using some accelerated plug-ins/ effects and while the PC can use that, enabling MP rendering on the Mac doesn't and sends everything in software-only mode.
We're actually using no plugins at all. Just the lighting effects and 3D layers like house-of-cards sets. As well, in the info it states that MP is working in both cases, and the Mac Pro, when it does render frames it spits them out 6 at a time, as per the render settings.