the x700's, x1600's, x1300's, etc. are not really a good value for gaming at all. You're most often better off with a lower end x800 card or x1800gto. I've yet to see where a card that was released as a mid-low end card is a good choice for gaming.
Now for HTPCs or everyday computing, the midrange cards are great.
But you should stick with the x800's, 1800's, 6600's, or 6800's.