This site is being deprecated.
Please see the official X‑Plane Support page for help.
X-Plane is multicore/multithreaded, and as far as I know there's no limit to what X-Plane can handle. If you use a program to watch how many or which threads X-Plane uses, you might end up disappointed. But the reality is: X-Plane goes as fast as it goes. Sometimes we're stalled on the CPU, sometimes on the GPU. However, in general if you buy top of the line hardware, you'll see better performance. I cannot make any guarantees about the cost/benefit analysis though. :)
There are a few articles (like this one) on X-Plane's developer blog if you're interested in more of the nitty gritty of the technical side.
This site is no longer being actively maintained.