Tessellation...the Radeon 5850 isn't incapable of it and tessellation is barely used.
Tessellation may be barely used so far, hoever it definitely is being used with variable settings from low to high in Civ V, and it will soon become just as common as pixel shaders, bump mapping and anisotropic filtering - I am completely sure that by the end of 2011, every new game will be using it.
I've used ATI cards for for over 5 years, and previously had a pair of 5770s. There was lots of testing and investigation being carried out for the DX11 and tessellation performance on the HD 5000 cards, and they foud quite simply that tessellation performance was very limited, and the same across the entire range - my 5770 crossfire would get exactly the same minimum FPS in tessellation benchmarks as rossfired 5870s or a 5970.
The HD 5000 range isnt incapable of tessellation, however its tessellation function is very limited. This is believed to have been due to ATI wanting to get the cards out asap to overtake Nvidia, while giving little thought to the tessellation engine. and Civ V definitely uses Tessellation.
Hey thanks for the help. For the record I was playing a huge multi-player map on a 60in dlp hd tv and I had the game cranked to 1080. Took back the 5670 and got a Ati 4870 so im all set now, sure no dx11 but its dx10.1 probably wont notice much difference.
IMO you should have gotten a 5770 really.
A useful comparison table of the various graphics cards:
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Heres a better place to compare:
http://www.anandtech.com/bench/Product/180?vs=164
The GTX 460 isnt very far behind, and costs a lot less than a 5850 does. Now in Civ V, if you turn Tessellation up to full, the GTX 460 will easily catch up, and maybe even overtake the 5850s performance.