I've recently revisited WOW,
currently running:-
e8200 @ 3.6
3870x2
4GB ram
Win 7.
with Vsync off just running around i avg 70-85fps in wrath zones. 100+ in old zones.
But i also have a gaming laptop running a core 2 @ 2ghz, 7950gtx 512mb and 2gb ram. and that averages around 50-60fps in wrath and 70-80fps in old zones.
conclusions?
warcraft it's self is the bottle neck? that you need to spend a lot for a gain or no gain if Vsync is on.