I've had great luck with Bridgestone Blizzaks on 3 cars and am getting a set for my Challenger this month.
I get tire/wheel sets from Tire Rack and just bolt them on myself. Try them for tire recommendations and wheel size info for your Xfire. They're happy to give you all the info you want over the phone. No pressure to buy from them.

http://www.google.com/aclk?sa=l&ai=C...21tirerack.com