In GPU-z its called VCC Phase I think. But not all cards support it. If yours doesnt, that would have me worried:
nothing like that with the sapphire xtreme 5830. GPUZ reports a gpu temp off by itself, and gpu temps1, 2, and 3 a bit lower in the list. all track to within 3* C, so I doubt any of them are a VRM temp.
the VRMs have a pretty beefy separate heatsink, and its an open case with an external 120 volt ~200 CFM 120mm aimed at it. so dig till ya drop baby! seems lots of this particular model 5830 are running in the 1000+ range and so far so good.
I do consider that particular card disposable though. no resale value to speak of and no use besides mining to me. guess we will see.