From what I’ve read, and from my own tests, I believe the following to be true. Would anyone care to confirm, amend, or refute these statements?
Max/MSP/Jitter only takes advantage of multi-threading if you use the poly~ object.
Poly~ only multithreads audio; running Jitter objects in the poly~ object does not improve performance.
If you open and run two instances of a program, they will still run on the same core (unless you are using poly~).
Jitter only takes advantage of a fancy graphics card if you directly invoke it using the jit.gl objects.
Max is a 32-bit application; running it on a 64-bit machine has no impact on performance.
As a 32-bit application, Max can only utilize 3 GB of RAM.
Given all of this, for Jitter-intensive projects, it's better to go for a higher speed dual core (e.g. Intel Core i5 3.46 GHz) than a quad core machine with a lower clock rate (e.g., i7 3.06 GHz).
It’s probably still good to go for a 64-bit OS with 4 gigs of RAM, to let Max use all it can and still have extra room for OS overhead.
Unless you’re doing sophisticated shader stuff with jit.gl, it doesn’t really matter what video card you use; any basic video card will do.
Thanks for any comments, corrections, clarifications, or suggestions!