Getting a new graphics card have more questions

I have read thru the stickies, etc here but with the new cards out I still have a couple questions. I currently have 2 nvidia gefore 8600 gt graphics cards sli and I want to upgrade. Newer games are not able to perform at high end, such as Empire total war. My system is a 2.4 ghz quad core Q6600 w/ 3gb ram, liquid cooled, PSU is COOLER MASTER eXtreme Power RP600PCAR 600W running Vista. My resolution is 1680 X 1050. I have a eVGA nForce 780i SLI 775 A1 Motherboard. I am looking at a couple diff options, whether it would be best to get the radeon 4890, 4870 x2, or the geforce gtx 275, or if one of their other models would be better. Also how do I tell if a card I like will work with mobo etc?I've read the reviews and Im still torn, I wanna get the best deal for my dollar of course. I'd like to not upgrade my PSU if possible, but if you think it's needed what do you recommend as replacement? So basically if you were spending around $300ish what would you do? Thanks for the help!

+1 rags


Depending on how you're going to upgrade:
The more cost effective solution is to get two cards for SLi since you have an SLi mobo. But getting the 4870 is also good.

If you won't ever upgrade the GPU after this, get yourself two 8800GTs or 9800GTs in SLi - that would basically be a GX2 and rival the GTX280.

If you have cash, get a good 750 PSU and get two 9800GTXs/GTX+/GTS250 in SLi

Don't get the 4850 since you can't Xfire on your mobo, and don't get the 4850x2 since it is buggy

New Egg has a BFG Geforce 280 for $20 more than the 275, is it worth it for the upgrade? if not Im just going to get the 275. And if I do get the 275 would you recomend the BFG Tech or EVGA? THANKS for the help!