Now that the 3870x2 is only 300 at newegg, i was wondering if it would run better in xfire than a single core 4870 in xfire, with two 3870x2's you get 4 cores running, even if they are one gen older than the 4000 series.

Well, a single 3870x2 should be faster than a single 4870.....

... But I'm quite sure a crossfired 4850 is faster than a 3870x2.....

.... But since if you can really find a Radeon 3870x2 in $300 or less. I suggest you get it. Unless you game at really high resolutions.

If i was willing to max out at $600-$650 in video card(s) how should i spend it? 2 4870's or 3 9800 GTX's or 2 3870x2's?

Well I think there may be some scaling issues with 3870X2 in crossfire. And all 4 cores have to communicate together, which might be a little more difficult than just standard crossfire.

If both are $300, I think I would go with 4870s in crossfire, because it would be more likely to scale well, easier to manage, and a newer, more forward looking architecture.

I'd get 2 4870s, xfire doesn't really scale that well beyond 2 or 3 cores depending on games, drivers...

go with 4870.. 3870 x2 is not that good in xfire.
and in all performance 4870 is better, takes lesspower, faster than any other card on the market today in CF or SLI

If your willing to spend that much wait for the 4870x2 to realease.

some games wont kick in the cross fire , I would get the fastest single card and crossfire that now or down the road when there well less $ like MrsBytch quoted you , so either the 4870 or the 4870x2 , in the future you will be happy you didnt get the 3870x2 , the way the tech changes now a days thats the way to go , have fun !