With your Mac Pro, you should have all the processing power you need. I have taken a more minimalist approach to mixing lately, and the only 3rd party plugins I use are from IK Multimedia, FXpansion, and PSP. Occasionally, I will get overloads, but since switching to Logic's native plugins for a number of tasks, I have avoided overloads for the most part. The problem is in Logic's relationship with 3rd party plugins.