HD 6850, should I double up or upgrade?

[JZoidberg]

I currently have a Radeon HD 6850 graphics card, and am looking for a bit of a step up in performance. I have an i5 3570k that I've yet to overclock (I keep telling myself I will), and am trying to figure out what would be the next best step to improve my computer. Really, just curious as to how 2 6850s would compare to a 7870 XT or 7950. I don't necessarily have a set budget and could buy any of the three cards, but I'm looking for the more economical choice. Sell my current card and fork out $250-300 for the 7970 XT/7950 or $140 for a second 6850.

 

[JZoidberg]

Oh wow wasn't expecting such a quick response. Thanks. I actually posted the question on another forum and got a different response (to go for 7870 XT or 7950). Know of anything to compare (specifically) the 6850 crossfire with the 7950? I've found a few that show the 6850 alone in comparison to others, but is it just a straight up 2x as effective if you have 2 of it?

Also, any recommended PSUs? My current one is 480 watts. Would I need any additional cables to run crossfire or just a second connector from the PSU to the card itsself?

 

[loops]

sell 6850 get 7890 LE...sell the games that come with that card....done

 

[JZoidberg]

sell 6850 get 7890 LE...sell the games that come with that card....done

I did see the games on the Newegg listing, but honestly I think I'd at least keep Bioshock. What would be a good market to try and sell the Tomb Raider one on, if I do go for that card?