Alterac Valley FPS

[defactoman]

Something seems to have changed since BC when it comes to my AV performance.

Here is my machine specs:

CPU: Q6600 Quad Core (AFFINITY: 1 wow per core for a total of 4)
GPU: OC GeForce GTX 260 896MB 448-bit GDDR3
Memory: 6gig DDR2 (at the most uses about 5.5)
Monitors: Primary 24" (Main Toon) Secondary 22" (3 Follower Toons)
OS: Windows Vista 64

When I enter AV and hit any large fight, my CPU cores max to 100% and my FPS drop quite fast to under 15 fps on the main (the others are forced to 15 fps). I seem to remember not having these problems when I boxed AV in BC but seems to be a pretty big problem now. Do I Just need to upgrade my system to be able to properly handle bigger AV battles, or might it be something else?