Firefly only uses the CPU for rendering. What you want is the most RAM you can get so as to avoid the program from using Virtual Memory, as that will slow things down to a crawl. As an example with RAM you might get 1,000,000,000 memory accesses a second, with Virtual Memory maybe 1,000. That is a big speed difference.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13