IIRC, 32bit windows will only use ~3.5gb of ram, so you'll need 64bit to get the best of the 8gb included with that kit.
That bundle includes a non-K variant of the i5, which I believe means you won't be able to overclock (this probably won't be an issue, just worth noting).
Tbh, I ran WoW on a 4850 at 1680x1050 with decent graphics settings for two years before I got round to upgrading, so if you think you can put up with it not being on ultra for a few weeks it might be worth using your old card and putting the money towards a better CPU? WoW in general is more CPU intensive than many single player games, and in many cases will be held back by the CPU long before it maxes out the graphics card.