yes the X1600Pro is faster than a 6600GT.
It came atleast 1.5years later and it does outperfporm the 6600GT.
If its a usefyl upgrade though Im not sure. I suppose it is if you get say R800 for your card and it costs R900 bucks then yeah its worth it.
Sorry, rather listen to Shock G, Im not even trying to back my little post up with facts. bets would be to check it out on tomshardware.com, they have the best graphices card reviews.
It just performed rather badly (relativley, much better than my PC still) in my friends PC and I doubted whether a 66GT could be any worse. But I'm not even shure if that was the pro version.