PCI-E 1.0 and 2.0

I know the 1.0 and 2.0 graphics cards are backwards compatible with each other somewhat, but how much so. I can't upgrade my motherboard without getting a whole new pc basically so I'm stuck with PCI-E 1.0. Should I stick with 1.0 cards, like the EVGA GeForce 8600GTS SSC, or go for 2.0 cards? My power supply is big enough for either. I want to SLI them.

Edit: I think I may have figured it out some, if I get a graphics card with a power cable to connect directly to the power supply I think it would work better then older 8600GTS SSC.

 

Ok new question. To sli on 1.0 slots what card would you think would be better G92 with 2.0 slot or this one that is 1.0. Although the motherboard I am wanting to sli on only supports 8x speed when sli. Should I hold up and get just one of the two cards and start putting towards a new system?

Edit: I have the updated pci-e 1.0 slots that support 2.0 cards.

 

either one will do just fine as long your psu is strong enough for 2 of those monsters No reason to upgrade board until you really have to.

 

FYI, video cards can not use all the bandwidth that 8x provides. They don't even use all the bandwidth on a 4x connection. Only at 1x do they start to lose performance. Tom's Hardware just did a benchmark on it.

http://www.tomshardware.com/reviews/pci-express-2-0,1915-9.html

So, I wouldn't worry about 8x vs. 16x. It doesn't really matter.