Windows 7: New card(s) help needed

Hi folks I need some advice on getting a new graphics card on which would be better getting a high end card or sli/cross firing two medium cards say like two gtx560ti against a gtx670 or two 7850s against a 7970
I used to have a 560ti but it wasn't good to handle what I want
Any help would be great I know they is alot of difference between cards of different manufactors i just want a basic idea

the higher end cards like the 600 series NVidia's and the 7000 series AMD's
are very powerful as a single unit - doubling them up is OK, but you don't really need to

I have two AMD6870's and they run extremely well together, but a single 7970 would do just as well..

I'm just trying to find between that card selection which would be better as general

To give you a little comparison, I had 2x 560ti's and a friend had a single GTX 670. His single card scored the same as both my 560's put together in 3D Mark 11.

Not sure if that helps, but heho

Thanks Paul that's what I was after

IMHO, it's also good to avoid the potential driver issues with SLI or Crossfire. I haven't experimented with either in years, but driver updates used to break them with discouraging regularity.

Anybody got any clues on the amd comparison

Just get an hd 6970 lightning and call it a day.

I need something better