http://autos.msn.com/research/vip/Spec_Glance.aspx?year=2009&make=Volkswagen&model=GTI&trimid=-1
You can punch both cars in and compare. Just taking a quick glance, it looks like they're pretty close on horsepower, but the Mustang has (had - yours is a bit old) a little more torque.
Is FWD better than RWD? Well, it depends. In the snow or slick conditions, FWD is generally better. On the race track, RWD is generally better. The GTI doesn't have massive horsepower, so you may not notice it, but a lot of higher hp FWD cars suffer from "torque steer": you get the feeling that the car is trying to steer itself when you're on & off the gas (not a fun feeling going through turns at speed).
For the money you're looking at, let me ask, have you looked at the Subaru WRX? The new ones are uglier than Rosie O'Donnell in a bikini (IMO), but they're hella performers and very easy to upgrade and tune. Plus, with the WRX you get all-wheel-drive and about 65 more horsepower and 20-30 lb-ft more torque than the GTI. I think the new ones are about $1000 +/- more than the GTI. I give it to the GTI on style points, but the WRX beats the hell out of it performance wise.
Unless you're just sold on one particular car, punch several cars into that site and compare. That's the best way to do it before you go to get raped... I mean, before you go talk to a dealer. Hint: arrange your financing and do your shopping online. I only set foot in dealerships these days to pick up the car and sign the final papers.
