Apples are now pretty much all using Intel processors now, so that advantage is gone when working with graphics/photos/video. I don't know enough about the Apple OS to say if that gives any advantage, but in terms of gaming, Windows certainly has a huge advantage, if for no other reason than all the high end graphics cards are supported first and foremost for Windows.
Edit: I just completed a new machine for the shop: 8 core AMD processor at 3.5 Ghz, 8 gig ram, 256 SSD, mid range fanless graphics card with 1 Gb video memory. I'll be loading up Win 7 Pro tomorrow or Monday, but I expect it will feel pretty snappy for a work machine.