Just published is some Newmont data in a paper at SAG 2011 on both SAG and ball mill steel consumption. The ball mill wear data reflected a 0.5 factor on the Bond equation consistent with Arts observation above.

The Amps in a mill are a derivative of the Kg/KWh, which is the ultimate most important indicator for steel balls consumption. When one make the integration of Amps vs. time one obtains the kWh, so those parameters are proportional, but also the kWh gives an indication of the mill efficiency.