Thing we have to appreciate here is that the cards are staggered in terms of their target purchasers.
We should know by now that x000 -> x500 are going basic cards in the range of the processors, wouldn`t mock em too much, they can make good multimedia cards. x500->x700 are the mid ranges, with some multimedia including inputs aswell as outputs - handle alot of games ~well~. x800+ are the top ends, great for spanking games and varieties do the below stuff too.
nVidia have been like this for a while.
If u`r some1 who buys a x800/x900 card "usually", like a 7900, if u buy a 8600 range u can only really look at it as a stop gap - u should be looking 8800 and above. Then again, if u struggled to purchase the 7900 - u should repeat the struggle to afford the 8800/8900 or u`ll be doing the same stop gap thing.
I like the x600 cards, I don`t play css at max frames etc and I appreciate some multimedia i/o. Some of them clock well too.