When you factor in the total cost of ownership (remember that socket 775 is out of date now) then 720 becomes a very attractive chip.

I don't think it will matter very much for games. The OP is going with a mid range 9600GT and is probably not going to play anything other than SCII. Extra cores however will potential save time on code compilation etc.

Like I said, the strength of AMD Phenom II is the relative low price and offers great upgrade path for the future.