I've not used ATI cards for many many years, but having a quick look, the X1600 Pro does look like it's got a higher spec than the X700 series......not by a huge amount, but it should be noticeable, I would guess.

Upgrading from 1GB to 2GB, I would say, may make a bit of a difference, aswell......but, then again, it depends on the game. The likes of Battlefield 2 and Everquest 2, I noticed a MASSIVE difference when I upgraded from 1GB to 2GB.