8600GT Number of PCI Express Lanes

I'm looking to build a system for trading and I need dual GPUs for 4 monitors. I'm trying to decide between a p35 MB and a p38 mb. The p38's all seem to have two pci express slots with 16 lanes. The p35's seem to have one pci express with 16 lanes and one with less (mostly 4). Do the 8600gt cards take advantage of the 16 lanes if present? If they don't, I may be better off with a p35 based system. If they do, then I'll probably want to step up to a p38 based system. Any feedback on this is appreciated. -- Bud