I use a i7 920 oc to 3.0 (150 base clock) , 12 gb of ram and a 1gb 4870 Ati (2 monitors). I use the 1680x1050 resolution on all 5 with the normal main set to high performance (minus shadows). I have very good results in northrend with 40-60 fps in questing areas on the main with slaves capped at 20. I haven't tested Dalaran on this machine since I came back from from my Wow vacation.

You will not have any problems once you get to 8gb of ram or higher.

Note: The 3.0 OC is great because the underclock feature still functions for power and processor savings. Go above 3.2 ish and it is prevented from functioning iirc.