I have pretty much the same problem when I run 5 toons on my new Intel Q6600, 2x2g Kingmax DDR-800 memory, 1x 8800GT. I don't have the extra 8800 that you've got, but I had no clue my guys would be struggling to get through Shattrath. I'm thinking about getting another 8800 GT, but i'm in the cross roads of xkeys, the video card or a new monitor.

X-keys: More control over my toons. I can start mapping abilities that I've neglected to use due to button space.

Video card: Will plugging in another 8800 GT (non-sli) make my toons run through Shattrath without having to pause every few feet for everyone to catch up? (no idea what kind of power supply i have. I was harping about getting "the best" and at the time i was under the impression a 450 W was good enough for 2x 8800 GTs. I hope it's enough.)

Monitor: I can move the 4 toons off my 22". I've got a 19" square mon, 22" wide, and i have no clue what size mon to get next. I just know the 4 toons on my 22" isn't comfortable, and playing just 2 toons on a 22" portrait isn't practical.