They Are different Chipsets
one is x38 (the pricey one) the other is P35, X38 is better than most if not all nForce Chipsets in terms of overclocking ability, most x38 and P35 boards can do only Crossfire... but you should wait before you buy.. new stuff is coming soon..
and PCI express and PCI are completely different, and you can't SLI on that board