I love both xfce and gnome versions. I find on a older p3 1ghz, that I use to watch media on my tv, xfce runs a LOT smoother than gnome. On a new ubber light speed fast pc, gnome or xfce will still flash at the speed of light. My main pc is a laptop AMD 3500 with 2 g of ram. Not a new dual core or something, but not to ancient. Gnome runs very well, but I find when I run XFCE it does not get as warm, battery lasts about 20-30 mins longer, and when I run games they run a much smoother.
Now doing the same thing on a quad core, and no difference would be seen for much. Then it comes down to preference, and I still have a hard time deciding between the 2 desktops, both are so nice.
So go with what one you like