SolusUmbra, the two most notable differences between Linux MInt MATE & Xfce are first, the Xfce version is a lightweight distro with less software installed. Whereas with Linux Mint MATE, you get a complete distro loaded with software & the ISO is just barely larger, and the OS hardly uses any more resources.
On the other hand, both Cinnamon & KDE uses more resources & looks much better on a newer computer with modern graphics. The newer, the better for those two.
You can always try both by booting from a Live DVD, or by creating a bootable USB stick, a 4GB one will do (I use a 2GB SD card attached to a USB card reader) for testing & install media in one. Once it's fired up explore the software & see how everything runs. One of the greatest things about LInux Mint is that they support non-PAE hardware (similar to your posted specs) with ease.
Simply take both for a test drive & determine which meets your need.
Good Luck with Linux Mint, if you go that route, you'll love it compared to XP in time!