PCI Express And CrossFire Scaling: Is P55 Good Enough? Toms articlehttp://www.tomshardware.com/reviews/p55-pci-express-scaling,2517.html
They use up to 3 5870s
Skipping to the conclusion
Yet, even though our motherboard of choice( for the x58) is slightly slower than many others, its dual-GPU CrossFire configuration provides 4% better performance than the P55 with identical graphics.You will gain 4% using an i7 x58 setup in crossfire. Is it worth it? You decide?