The problem with graphics cards atm is that the majority of games made are console-oriented. So a 5870 may be 6 times more powerful than an xbox360/ps3, but if games are being tailored for the limitations of console hardware they are not going to stress the gpu. There are a very small handful of games that are pc-specific and do stress hardware like STALKER, but even those are easily maxed out with a gtx285. So I'm not even sure in a year's time we'll see games that will choke current generation hardware. It used to be that you absolutely had to have the most up to date graphics cards because there was always something on the horizon that would demolish what you had running (doom, quake, half life 2, doom3 etc), but I don't think it's the case any more. Even the next Crysis and ID games are being ported to consoles. You think they're going to push your 5970 to its limit? No chance. Valve is content with squeezing Source till it hemorrhages. So where do you see this mythical next generation of graphics coming from? I can't see it anywhere on the horizon.
Amongst the most sensible posts I have ever read here on MyBB.

You're very right, we play more console ports now than ever before, even Alan Wake that was supposed to champion DirectX10 when it was announced many years ago is now a Xbox360 exclusive. The truth is the PC as a gaming platform where visuals are concerned offers almost zero value above the consoles for developers. To keep turning up AA is meaningless past 4xAA (MSAA with Transparency). At 1920x1080 it's as smooth as most people would ever need the image to be. 16xAA needs the screen resolution to increase in proportion and very few ave displays capable of more than 2560x1600, in fact most graphics cards will not drive a higher resolution. So even more AA of no value at all, investing in a $700 5970 to play the same game as someone on a $199 console because you can use 8xAA at 1920x1080 is insanity. Increased AA modes will not make the game look any better, a 512x512 texture remains so regardless of how many samples you take from it.
I have been using 5970 for a while now on one of my machines, but I prefer to game on the GTX285, and only for two reasons. PhysX and 3D Vision, the two things not even 2x5970 can give me.
I am playing Avatar and Shift right now (just finished batman) and those game experiences are significantly different enough on the PC (with 3D Vision in particular) to make it worthwhile adding a second GTX285 to the setup. One woudl need this extra performance purely because enabling Stereo 3D has a performance hit. On a GTX295 however, I can enable 3D Vision just fine and still maintain my native 1920x1080 res with 4xAA and its butter smooth above 50fps. (Most of the multi platform games we play are usually at locked to 30fps btw)
To run a 5870 in Crossfire gives me nothing but a higher frame rate which I never needed in the first place because that card is powerful already. With all the displays I have available to me limited to 1920x1080, frame rates move from an already way more than adequate 70fps to 102fps. This boost in frame rates does nothing to enhance the gaming experience at all.
Hard to find a game that can't be maxxed out on a GTX260 216, at 1920x1080 no AA (this is the Xbox mode as well as AA is only on SD resolutions) so how one ends up justifying a $700 purchase for gaming purposes purely is beyond me.