Cf 7850 or gtx 670 or gtx 680?

Just buy a second HD7850.The two cards in crossfire will often outperform a GTX 680!And you'll also save quite a bit of cash.

If you already have something in mind about what to do with your 7850 (like selling it for not much loss), I would suggest the 670 which is best $-performance wise. It also open the possibility for a much more powerful dual card configuration (SLI) if you feel so incline in the future.

But if you can only dispose of the 7850 at a considerable loss, then I guess considering a 2nd 78509 for CF is not bad idea at all.

CF 7850=FTW!

How much more powerful is the 680 compared to the 670?

Not by much. Please check the benchmark results between a 670 versus other cards (including the 680) here:
http://www.tomshardware.com/reviews/geforce-gtx-670-rev...

Short version: Two 7850s will be faster than a GTX 680. Because you already have one, I see no reason to recommend selling it and getting a 670/680. Get a second 7850 and crossfire them, assuming you have the space on your motherboard to have a slot in between them so they can breathe.

Long version: The only caution I would have about it is that there's not much info out there on 7850 crossfire performance. I don't know if that means anything or not, but you can always run into issues with a dual-GPU setup (stuttering/finicky drivers/etc).

Point is: You don't really have a bad option between 7850 Crossfire and the GTX 670. That GTX 680 price is way too high compared to the 670 and I wouldn't recommend that at all. However, if you like your 7850 and are not too worried about the potential issues that can crop up with (any) multi-GPU setup, then that's the best option.

If avoiding those potential issues is important to you, then it may be worth it to go through the hassle of selling your card and getting the 670 even though its performance will be weaker overall.

Ok. If I were to buy a gtx 670 how would I hd 7970 compare?

Also Im playing games such bf3 crysis etc

Best answer selected by gab10101.