P35 or X38 motherboad for running 2 x HD 3870's in crossfire?

[Jamz]

Ok so I already have an ASUS P5KC motherboard and I want to run crossfire with 2 x 3870's.

I know the 2nd pci-e slot is only 4x on my board and won't perform as well as an x38 motherboard that has 2 16x pci-e slots.

My question is that is it a big difference in performance? big enough that it would be worth upgrading to an x38 motherboard?

I've read this thread
P35 vs. X38 Crossfire performance comparison - Forums on the BleedinEdge
where someone did the comparison between p35 and x38 running benchmarks on 3Dmark but I'm more concerned with real game fps performance.... I'm not tech savvy enough to know how those benchmark numbers would translate into real game FPS performance.

[belgolas]

you would see a good margin of a performance boost. I don't know if it would be worth the couple hundred more for a new mobo though. It might be cheaper to sell your card and get a 3870x2 instead of buying a new mobo and GPU.

[Jamz]

Originally Posted by belgolas

you would see a good margin of a performance boost. I don't know if it would be worth the couple hundred more for a new mobo though. It might be cheaper to sell your card and get a 3870x2 instead of buying a new mobo and GPU.

I've been debating whether or not I should just buy a 3870 X2 instead.... but it's hard to find one less than $400.... i could probably score another 3870 for around $150 and then upgrade the mobo for under $200 (I'm suggesting used prices here).

in both scenarios I could recoup some of the cost by either selling my current mobo or selling my current video card....

would be even worth it to go crossfire with the 3870 and my current motherboard?