Most areas of FLEx does not take advantage of multi-core processors but there are a few areas that do.
The Dictionary Preview and upload to Webonary both use multi-threading when generating the preview content. More cores should increase the speed in those two areas in a proportional way, we increase the number of threads that we use if the number of logical processors increase (which is tied to the cores). The more processors available, the more threads we will use, which increases the speed for that view.
It is possible we will take more advantage of increased core counts in future updates, but we don't have any concrete plans for that at this time.
We do not make any special use of graphics processors. So the benefits will only be the same as any .NET application would see.
Regards,
Jason