Macs vs. PC is pointless. I think why people in 2D graphics use Macs is that they look more pretty (according to most people, not me) and the people doing graphics always have works of art hanging around their studio so having a generic beige box will spoil the evironment.

From a hardware point of view, both a PC and a Mac using Intel will have the same processors (if you know where to look, you can buy dual or even quad socket Xeon system boards with support for 32 GB of RAM for PC), the same graphics cards, the same hard drives, the same everything except for case and bundled OS. In my opinion, most the performance from a Mac comes from its OS, which is much more better at given itself a smaller footprint, unlike Windows which suffers from software bloat and other stuff, although you can just get yourself Linux.