I will say that I've had longer 'relevancy life' with a Mac than I've ever had with a PC, and PCs don't seem to be getting any better on that scale. My work computer is almost six years old and it's finally needing replacing now-- but I do an asston of Photoshop work on it and it uses a lot of memory. That might be something to take into account.

Having said that, my laptop's a PC.