On a Mac, you'd find these are much better. Things like fonts, robust interface, better mouse tracking (without spending tonnes of money on a good mouse), no Blue Screen, no Virus, and the blardy OS know which type of app opens which type of file. i.e on a PC, the stupid system doesn't know that an Illustrator EPS file should be open by Illustrator while a Photoshop EPS file should be open on Photoshop. On my current Dell, the whole EPS files and some other files are screwed up. TGA which should be open on Photoshop now runs FormZ (3D software that uses TGA format) On a Mac, I've never encounter such a stupid problem.

Performance wise is pretty much the same. Those my machine is 0.05 seconds faster than your machine isn't going to help you that much. Color management is easier on a Mac.

Once you use a Mac for designing, you might understand. I've used both platforms and I can say for sure that the whole interface feel and 'something I quite can't explain' is different. Plus the Mac doesn't have that stupid 'Windows Start' key on the keyboard.

What does design gotta do with graphic card and sound card?