I'm new here (just got my xfire yesterday) and just left my 06 350z. I can tell you two things:

1. Xfire is better built with a more appealing interior

2. 350z is WAY faster...no contest.

I was able to take my 350z to the track and pull 13.8's consistantly all day and at texas world speedway had it ticking 153mph on the banking. I can't see my xfire doing either of those things. But, when I get into the car for my drive to work tomorrow morning, I'll be welcomed by a quieter ride and nicer interior than the 350.

BTW, as far as handling, it's a tossup.