Please don't let WoW decide what computer you buy. I've made that mistake, and it led to me dumping my old MBP (it ran too hot for my liking, a 2007 model) for another Windows laptop.
Now I've quit WoW guess what? I'm back to using a Mac...
Worth saying of course that Macs can game just fine, especially when it is something like WoW that comes in a Mac version too. My 13" gets very nice FPS (I installed it to test it out before my sub expires, I just wanted to finish the midsummer stuff).
It's just.. there's so much more to using a computer than playing WoW. Having a Mac, for me, just makes every other task that bit more enjoyable, and don't even get me started on the amazingness that is iLife
A computer you buy now will outlast WoW, believe me (can you really see yourself playing in another three years?). If you've been playing for four years (3.5 for me before I quit) you must be tiring of it; tiring of Blizzard introducing hard modes to make you do dungeons four times instead of giving four dungeons to work through etc? And all this nonsense now about swapping faction etc... WoW is dying a death and they're trying to rake in as much cash as they can; it's obvious that the developers are all on their 'new MMO'.
And you'll never, ever, ever get a 100% smooth gaming experience from WoW, no matter your rig. The biggest bottleneck now is the hard drive speed - loading up all the NPCs in Dalaran and the like - and unless you play from USB there's not much that can be done.
So have a serious think about what you need from your next computer; and try your hardest to put WoW out of your mind if I were you. Any of the new MBPs will play WoW just fine (as said I'm on a base model 13" and I've been very impressed with the FPS), don't overspend because you think you need top spec for a game you might not even want to play before long.
Think about portability too etc, whether it'll become important to you with your job to have a smaller machine, and battery life and the like.