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.