WoW, especially raiding, is the rare cpu bound game. I played WoW with a 5870 at 2560x1600 resolution max settings with no problem, but raids still lagged.
the g630 does quite well with WOW. as wow only takes advantage of two cores.
ive played wow an a g650 and the card was the bottleneck there. for sure. the card was a 5770. it came out of my computer which has an i7 950 and the g650 was getting 95% of the same framerate. the extra 5% is surely due to tripple channel ram and background processes having more headroom. this was all at 1920x1080.
that system should be fine i bet it will perform better than you think. the g630 is on the tomshardware cpu charts. check it out.