those old q6600s are BEASTS, lol. I know a guy who's still running one and doing fairly well at modern games with it, esp. if they are threaded. If you can do the bsel mod, you can get them running at 3ghz with very little danger, which is quite nice.
I actually don't think the curve will remain stable over the next few years, but yeah, at $27, it's a good deal even if you have to upgrade tomorrow.