for the same result on OLDER cards you need high Quality bumpmap textures and this kills the Vram bandwith means very very slow!
if you use lowend textures near by zero and tiny dose of tesselation you save much on Vram bandwidh means you cann put lowend RAM on the GPU or use a IGP for the SAME result!!
yes if you wana have much better quality result you need a huge GPU but lowend gamers don't care they wana have nerly the same result on less powerconsuming and less vram-banchwidh because thats save money!
in the past vram bandwidh (hugh bumpmap-textures)use kills the IGP and lowend GPU's
AND!!!!!!!! Bumpmap textures don't work on stereoscopic 3D output ;-)
so you NEEED Tesselation for 'stereoscopic 3D' support
or you will have very very ugle games in steroscopic3D view ;-)
the people just think about playing 3D games if they watch a HD5870
but they miss the part that the HD5870 is one of the fucking fastest OpenCL cards... around...
So for which games you want to use that card now? When you want to play dx10 games you can buy a 4850 too which should be much faster.
I do not "use" ati in the normal term. I test fglrx with hd 4 and hd 5 series - and i compare drivers Linux vs. Win. And of course video accelleration...