I'm basically the same system.

i7 920, stock speed.
12gb mushkin ddr3 1600mhz
Geforce 275 GTX, 896mb.
150GB Raptor, 10k rpm.

I have the main capped at 60 FPS, and the slaves at 30 FPS.

In Dalaran, I get 20-30 FPS on the main, and honestly the slave windows are too small to read what they're running at.

Outside, in most zones I get at least 50 FPS, but it spends most of its time at 63.2 FPS, which appears to be my maximum, with a 60 FPS cap. Slave windows appear smooth to the eye, but the actual FPS number is too small to read.

On patch day, I was seeing 20-40 FPS, in the outdoor zones that normally give me 63 FPS. It has since gone back to normal.