I just wanted to post here for anyone feeling discouraged reading this thread with similar hardware or looking to get similar hardware.

I have /exactly/ the same setup as the original poster and it's working beautifully for me.

ASUS P5B Deluxe
Intel Core 2 Quad Q6600 @ 2.4 GHz
4x2GB G.Skill DDR2 800 (8GB memory)
2xSeagate SATA 250GB Harddrives in RAID 0
NVIDIA GeForce 8800GTX 768MB
Vista Ultimate 64 Bit

I run my main instance of WoW on maximum settings @ 1280x1024 and the other four instances at default settings windowed into quadrants of a 1280x1024 display. Maxbkgfps set to 15 and maxfps set to 45, my main window never drops below 45 (which is a very seamless frame rate). None of my hardware is overclocked, none of my software is tweaked, I'm sure I could change things around for even better performance if I needed to.

I set the processor affinity in keyclone and symlinked my WoW directory (excluding the WTF folder and the Wow executable) using Vista's mklink.