One thing worth saying is that currently architecture differences aren't that major and performance is similar given similar hardware on mac and pc. Much more important now are usability features. One good thing about PCs is that with the number of manufacturers, there's a better chance that one will make a product you like with features that don't exist on the Mac.

For instance, Apple doesn't make a tablet that's really suitable for artists. The iPad lacks accuracy and pressure sensitivity. I was always surprised they didn't make one, as they'd then pretty much re-monopolize the art market. Generally I find artists think macs are better for them regardless of any truth behind it. All of my arty friends have macs for example, and to my knowledge only 1 or 2 of them use it for art in any way.

All that said, Windows 8 seems to have a lot of options that fill that void (see my other thread on the new samsung tablets). I think having any light tablet with an active digitizer that easily functions as a laptop as well is, for artists, far more important than any difference between mac and PC (unless you find it difficult to use either's default UI to the point that one is not an option for you.)