GS, GT or GTX

Is GTX 295 more powerful than a GT 9600, Radeon 4870 x2? I have two Radeon HD 3870 in a crossfire config and I want to upgrade to a single card. Which way do you recommend I go?
Flight Simulator and other chat
https://forums.simviation.com/phpBB3/
https://forums.simviation.com/phpBB3/viewtopic.php?f=9&t=27094
Here's my rig:
2.20 GigHz AMD Phenom 9500 Quad Core
Board: Asus M3A32-MVP DeLuxe3072 Megbytes Memory
620 Gigbytes Free Space
ATI Radeon 3800 Series (2x)
450W PSU
Is this going to hack it with the GTX 285?
Also you said that the two video cards crossfired only operates at half the capacity each. If I remove one of the cards since it's only running half speed, will I get 100% performance from the remaining card? I need to free up some PCI slots.
Bubblehead