For anyone who's interested; I've forked the radeonvolt project and made some cosmetic changes to the code. Well, one functional change in that the program isn't restricted to the HD5850 anymore. It should accept all ATI cards and check to see if the correct VRM chip is in use, and try to proceed if it is.
Also, the subvendor (XFX/ASUS/Sapphire etc.) is now displayed with the device information, and a --debug option has been added that prints out extra (more or less necessary) information.
Github pageI'm still trying to find out if GPU-Z can read the VRM temperatures of my card, because if it is, it should be doable in Linux too.
I have an XFX 5830 that it would be neat to be able to use radeonvolt on, and an asus 5870 (Which I expect less, as I know it is a super-special voltage regulator), and asus/HIS/HIS iceq-x 6870's. Let me know if there is any test info I can provide from them :p