I'm looking at getting a used system via craigs list with a 4890 vapor-x card in it. I don't play super intensive games, and am fine if everything isn't maxed out, but is just good. How long do you think it will be able to play modern games. 2 more years? Is that being optimistic? Right now I mostly play starcraft 2 and dragon age 2, but would probably get skyrim with the new system.
The processor is an x58 i7-920, which is also a bit dated, but I figure powerful enough to last at least a couple years, especially if I overclock it.
a 4890 is as powerful as modern low-mid range cards (between a Radeon 5770/6770 and 6850) but lacking direct X11. Best guess is in 2 years you may be playing on low settings but should still run the latest games.