Sorry for my delay in response. To be honest, I haven't been able to read the full thread yet so I might be redundant.
I have 32g of RAM and a 3.4gHz Intel Quad Core i7 CPU (iMac). My programs are installed on an SSD, my projects are saved on a regular 1TB hard drive, and my samples are loaded on a 4TB G-Drive with a FW800.
There were around 44 separate tracks, but they never all play simultaneously.
I can load a ton of samples but load more than 3-4 instances of PLAY and it just keeps overloading. I'm in the process of learning how to use Reaper. Have you found that PLAY works better there? I currently use Logic 9.1.8 and to be perfectly honest it is more or less capable of doing most of what I want to do.
With the kind of power and RAM your computer has, it's strange that you're having issues but it might be due to having your samples on an external. I have a Mac Pro 8-core with 32 gigs of RAM and am also using Logic. I can run PLAY without any problems at all for the most part. There's a problem where if a project is loading, PLAY will sometimes not load the patch but I think it might be due to attempting to type while loading a new session. But I've never had PLAY overload before. I did have a problem similar to this with the Cakewalk Dimension plugin but that was after the Apple OS changed and Cakewalk ceased supporting it on Macs.
I mentioned Reaper just in case you were on a PC and using Sonar which, in my experience, blew when it came to sample ram management.
I'm pretty confident that if I were to replace my PLAY percussion libraries with CinePerc, I wouldn't have any problems with the CPU overloading, but i'm not sure if that confidence is unwarranted. Do you think it's a problem with Logic?
I don't think it's Logic because my own set up does just fine. And you have a newer CPU set up than I do. The only difference is that my samples are on an internal HDD and you're using an external. The graphics point might be part of the problem for sure! But I'm willing to bet my video card is lower spec than what's in your iMac, just due to the age of the computer, and I can float windows just fine while running PLAY. So it may or may not be it.
Side note: I am having the Logic EQ freeze up bug randomly, both in 32 and 64 bit mode. I tell ya... I love Logic but with the way things are going, if Apple doesn't do a serious update to Logic soon, I might just go to Cubase.