I'm not sure of the answer to your question, but I run all my fans straight from the PSU. I believe it aids stability.
I bought HDD style molex plugs from my local electronics shop, snipped off the smaller plugs from the fan's cables, and soldered on the new molex connectors. As a result, I do not have RPM monitoring, but I never used that anyway.
I checked the fan I was using on my mp6 and they suck 0.12 amp each I did not use the 3rd fan header so I'm not sure of the limit but 0.5 amp seems to be stciking out in my head for some reason as a fan header limit for the board. I don't even know if that if for abit boards tho.
InaxtiveX, when you snip the wires on a fan with the yellow rpm wire, leave the rpm wire. power the fan on molex and plug the 3 pin to a mb connector. It should monitor the rpm.
Dual Barton Mobile 1.8ghz
Venice 3000+ @ 2.6ghz
lots of BP6s and two VP6s all apart currently