I'm using Linuxcoin but overclocking features seems to be less powerful than those available to windows.
I will try a portable XP soon, see if I can rise my 5830's 260Mhash/s to 300Mhash/s.
Hmm - I also got 260 MHash/sec under Fedora 14 and AMD openCL v2.1 - is this normal then?