Thanks a million guys!
I've been mining for about four years now, just using three old family computers that were laying around here. Although I am profit conscious, the fun factor is also very attractive to me. If I do build a new rig, it will also double as a family computer.
So if I have this straight, PCI bandwidth isn't much of a factor for GPU mining. Without risers, any x16 PCIe slot running at x16, x8, x4 or even x1 will work.
Thanks for the Biostar suggestion . . .