3dmark06, 1280x1024 default. Windows Vista.
Q6600 number 1=2997 Mhz; score = 4277
Q6600 number 2=3330 Mhz; score = 4764

Well ok, that's to be expected.

2 x 3870 in crossfire:
SM 2 = 6195
SM 3 = 7609

a single 3870X2:
SM 2 = 7035
SM 3 = 8134

Simply because the CPU is slightly oc'd you wouldn't get such boost in SM performance in crossfire.
This card performs better than 2 x 3870 in crossfire.