Even tho it should run smooth, maybe it doesnt like crossfire/sli ?
On my Geforce 580GTX it runs smooth as everything else I throw at it.
My spec is older, but still going strong:
ASUS Maximum Formula II Motherboard
Intel Core Extreme QX9650 @ 4.1 GHz
ASUS nVidia Geforce 580GTX @ 840 MHz
8 GB Mushkin eXtreme performance (DDR2) @ ~1100 MHz
Everything watercooled by the best components on the market (Thermochill radiator, EK blocks for CPU, GPU, NB/SB, MOSFETs, RAM)
Game is running of a WD Velociraptor 600GB disk.