Regarding PCI express, you'll find that many older SLI motherboards (allowing two graphics cards) include two PEG slots (ie. two full size PCI Express grpahics card slots) but didn't give maximum bandwidth. This was because last generation northbridge/southbridge combinations only offered (say) 24 lanes, as they thought "16way for a grpahics card, and 8 lanes for everything else".
As such, many systems are already running graphics cards in slots which are 8x not 16x, and it didn't limit choice of card nor performance (to any great degree). Indeed, it was only latterly that nvidia issued a version of their Nforce 4 chipset with 2 full 16x slots.
Only last week I was reading about the lane arrangements on the most recent Intel 975 boards and ATI R600 systems, which in some cases still didn't offer 16x to all PEG slots (although to be fair, they are now talking about having 3 PEG slots on a single motherboard, to allow for a third graphics card for physics processing).
Translation - number of PCI express lanes isn't really that big a deal right now, and won't (shouldn't) affect choice of available cards.