Newer generation cards do support more things - just the mid-low range cards are just designed to perform worse (also allows older stock to be cleared out), but they will generate less heat / require less power than high end cards.
My 4670 performs well, except the fan's a bit noisy for my taste (so I disconnected it + downclocked the thing as far as I could push it down).  Probably wouldn't use CrossFire though - since you did a trade, I guess you didn't have much choice, though if you were to buy a new card, would've gone for a single higher end card (ie 4850) since it requires less power.