If you look at the standard pricing you seem to get a better spec PC for your money compared to a Mac, a lot of what you're paying for is the Apple brand.
If you've got a huge amount to spend and don't mind paying a hefty premium, then you'll get a product which does the job a little bit better. If you opt for the PC route then you'll get a machine that you pay less of a premium and aesthetically won't be as pleasing, nor will it be as simple to use. However, from a performance perspective, I'd have thought the PC would have had the advantage.
Adobe actually said themselves that there is no performance difference between their software running on a Mac or a PC, the programmers didn't type code that runs better on one operating system than another...
Being as Macs are now built on an Intel platform anyway... the only *real* difference between a Mac and a PC is the OS, and you can actually install OSX on your own-build PC anyway, some people had performance issues when they build their own, (BUT THIS IS A LIMITATION OF OSX, NOT THE HARDWARE) due to the fact the OS didn't strictly support the components they had selected... (drivers etc).
On top of this, a new Mac Pro is not upgradeable like the old model... meaning if you want to increase the performance you'll have to buy a totally new machine... Whereas with a PC you can choose to upgrade individual components, and on the next major upgrade you'd likely save money as you probably wouldn't need a new case, power supply, optical disk drive and fans.
So... if you're willing to pay more for aesthetics (when you can get some stunning PCs anyway), a brand, and an OS you could run on your own build anyway, then go for a Mac. If you're happy to pay less for a machine which has greater hardware choice, is cheaper, and will "do the job" just as quickly, then choose a PC.