PCI Express 2.0 into the 1.0 slot...

Ok. I have a motherboard with a Core 2 Duo 3.16ghz, 6 gigs of ram, and 550w power supply. I currently have a 9400GT since i only have a PCI Express 1.0 16x slot. So here's my question. Either what's the most powerful card I can buy for a 1.0 slot, or, although I know buying a PCI-E 2.0 card can still work in a 1.0 slot, are there benefits from buying the beefier card? Ultimately without replacing the motherboard yet, I want a graphics card that can do more, a lot more than my 9400GT. Any ideas? Suggestions?

So, we're not to the point where anything we could throw at the 1.0 slot could bottleneck on it? If this is right, how long do you suppose it will be before we hit that barrier? How much bandwidth does, say, a GTX 285 utilize vs. what's available on 1.0? This topic really interests me.

Here ya go. I know its old, but it is still an interesting read I think.

http://www.tomshardware.com/review [...] ,1915.html