Yesterday, I emailed Viahardware.com's Jasper about the test bios and he posted an update. He even mentioned my name! Anyways, he said that according to some forums, the test bios increases memory speeds and allows for higher overclocking.
Edit: Jellybaby,it is test bios though so I guess we can't expect much. As always, it's just use at your own risk. It would be nice, however, to get some documentation.