Honestly I don't know as much about pc's as I wish I knew. Not only that but with new tech being delivered weekly it seems, it's hard to stay on top of what's best. As far as changing, it has more to do with power saving than actual PPD gained from folding.
Rule of thumb for video cards is the higher the number, the better the performance (in 99% of the cases) All of my examples below rate the better video card at the bottom and the lesser cards going up.
So, for example, last year ATI came out with the Radeon HD 4xxx series cards in this particular case, the 2nd number represents better performance
it breaks down even more, looking at the 3rd number you see that some are lower than the others. In this case, the higher 3rd number means it is better than the lower 3rd number.