I can't say that Xfce spin is slower or faster than the LXDE spin of Fedora 13. The thing to remember about both of these Fedora spins is that it's easy enough to add any or all of the applications from one spin to another. I'm not sure exactly what the LXDE spin's policy on GTK 1/2 apps are, but on my hardware it looks like it'll come down to personal preference and not vast performance differences. The more I think about it, I'd be very happy to have both of these "spins" on one installation, and if there are metapackages for both the Xfce and LXDE spins (and I'm fairly sure there are), that's just what I might do.