Well, I've tried both Ubuntu, Xubuntu, and Kubuntu on my older computer, and the experience hasn't been that great. The specs are 800mhz Celeron, 128mb ram (no idea what kind :\), and a 30gb hard drive, and it came prepackaged with Windows ME (*shudders*) back when I bought it.
Ubuntu: I installed this back in 5.10. I messed some things around (apt would give me a lot of errors) but eventually got everything working. The only problem was that gnome was so slow, Firefox would take around 15 seconds to launch and would lag like hell when MSN was open at the same time.
Xubuntu: This was faster, but nowhere near as polished. It seemed that the window bar would only go halfway across the screen unless you used the default one, making an application launcher was a pain in the ***, and I still don't know how to make a shortcut on my desktop using xfce! Eventually, I used nautilus instead of xfce as my desktop manager, and the speed difference wasn't noticeable. However, it didn't feel very polished and user friendly, so I eventually ended up installing Kubuntu, hearing that it was faster than the regular.
Kubuntu: The speed difference wasn't that great vs gnome, I had a lot of the same problems. I do, however, like the user interface more than gnome when it's customized.
So my question would be: Is Mepis3/6 noticeably faster than Kubuntu, or should I just go back to Xubuntu or seek another distro?