Radeon 7770 Crossfire on x16/x4 board?

Today I got a Radeon 7770 (I wanted a 7850 but whatever). I have almost enough money to buy a second card and Crossfire it. My board however is only x16/x4. I know that when Crossfired the 7770 performs pretty well. What kind of performance hit would I see by crossfiring the two cards on this board? I don't care about micro stuttering or any bottleneck (I will probably get an FX 8350 down the road) just the performance I would see. Can I do this? Thanks.

Current Card: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Current Motherboard: http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Radeon 7770 Crossfire Review (Older, should be a bit better due to current Catalyst Drivers) http://www.tweaktown.com/reviews/4572/sapphire_radeon_h...