Wow... Sit down and take a breath.. You gotta be worn out after typing that much..
In all honesty, I'm in the same boat, but with a EVGA 680i. I mean, the 9600gt is a great card, but at this point I'm starting to hit games that won't max out.
Some answers though. The 8x 8x config would slow down the system a little(with 8800GT's or anything higher), but I'm really unsure of how much. I've read some people saying they're only getting like 1500 more points in 3D mark after the second card was installed. Then I've read others that are completely satisfied. And I have no first hand experience in 8x 8x config's.
What I would do for now though, is put your money into making your Quad run. You have it already, might as well be using it. You can run those on 650i boards, and they run good at stock settings. It's when you get into OCing that it becomes a problem. But if your not doing that, then no worries.
I myself think I'm gonna go the way of the 9800GTX also. More for Folding then actual gaming, but still... lol
Another thing I want to mention. I have a GeminII, and they aren't very good unless you lapp them. Once I did that, and put 2x 60CFM fans on there, it works great. But if you don't want to deal with lapping, then I wouldn't get it/use it. There are MUCH better coolers out there for cheap!
I came to the same conclusion as you though. With having a SLI board that handles the Quad wonderfully, I want to stick with this board until the new socket arrives. The CF board I have doesn't run the Quad quite as well, so I don't think I wanna go back on that..
Did I just make a long rambling again??
EDIT:
Short Version:
Get a 9800GTX, or even just do a SLI setup. You can get a GTS for ~$100 now, probably cheaper on Ebay/forums. Keep your Mobo till your ready to put a good bit of $ down on one.