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It's not the problem with the GTX480...it's the Q6600 not being fast enough running single/dual thread.
People that say Q6600 at 3.0GHz is not a problem with WOW...have you actually used one to play the game?
Most mmorpg is either single or dual-threaded, so a faster dual-core would deliver better frame rate than a slower Quad core.
There's a mmorpg I'm playing (not WOW) which my minimum frame rate would drop to 15fps at 1024x168 when there are many players on screen, even though my GPU usage is only around 20% max. I have a friend who got a Phenom II 965BE at stock speed 3.4GHz and with a 5850 playing the same game as me, and his minium frame rate is also lower than 20fps.
This is why i5 750 or i7 920 overclocked to around 4.0GHz will deliver higher frame rate in most mmorpg, because they are the fastest running single or dual-thread operation.
mmorpgs are always tend to be more CPU dependent than GPU.
I disagree. The gtx480 needs more than a 3Ghz cpu to run at it's max framerates in ANY game and WOW is very cpu dependent.
I know this is quite old with an Ultra 8800 but even then, a 47% increase in cpu speed = 41% increase in minimum framerates which looks pretty linear to me.
http://www.pcgameshardware.com/aid,631615/World-of-Warcraft-CPU-and-GPU-benchmarks/Practice/
And although is doesn't show you too many old cpus, this gives you some idea how important the cpu is in WOW.
http://www.anandtech.com/show/2901/13
Bascially at 3.33Ghz an i7 shows a 21% gain in fps over the same speed E8600 and an i7 at 2.66Ghz shows a 25% over a q8400 (comparing quad vs quad) and an i7 at 3.33Ghz shows a 21% gain over an i7 at 2.66Ghz (25% overclock)
Cache and the latest cpu helps a lot in WOW.
Those tests were done with a 5870.
So a "better" cpu with lots of cache running at 4Ghz+ and you would probably see a 50% gain in your framerates.
You have quite an unbalanced system IMO.