Well, I left out the slots on the mobo because it's not relevant, really. Someday when I build my gaming rig I'll want to configure everything in SLI/Crossfire, but for now, any game I'm playing will work just fine with with just one GPU. For the record, the mobo has one PCIe x 16 slot, and the rest are PCIe (x 1).
I want to get two of the same card, because my experience with NVIDIA cards (granted, running XP, and this new machine is Vista 64-bit) is that both cards end up using the same drivers, so to avoid any PITA driver-wrangling, I figure it's easier to use two identical cards. I was looking at another machine that had a dedicated graphics card already (9500 GS), but the store didn't have any aftermarket 9500 GS (only GT, GTS), and the doofus at the store said that the 9500 GS used different drivers than the 9500 GT.
Long story short, if all the 9xxx cards use the same drivers, that makes it less important that I run two identical cards. And on my current machine, one card cannot push 2 monitors @ 1680 x 1050 resolution (at at least 70 MHz--any lower and the flicker gives me headaches), and my reading of the max resolution the 8xxx or 9xxx cards was that they couldn't, either. Then I did the math and yeah, the max resolution on the 9xxx cards can handle 3360 x 1050.
Since you say the drivers are the same for all 9xxx series, I'm tempted to get different cards. As far as having only one PCIe x 16 slot, aren't PCIe x 16-capable cards using the same interface, and can "clock down" to use a PCIe x 1 slot?
Sorry if that last question is idiotic, but I thought most cards were backwards-compatible; i.e., AGP 4x cards worked in AGP 2x or 1x systems (just with a slower interface).
I'm opening up the case in a few minutes to put in the new PSU. I'll see how much room there is... that's the problem with ordering parts online, though: it might look like a tight-but-doable fit, but when the stuff arrives, you see that it's too tight.