The carbon shoe won't wear as long as the alloys in a mixed set up, it's not meant to. I would think you would wear through 2 or 3 carbon shoes per set of alloys maybe ?
Torn up clutch bell what happened there ??? Shouldn't have been anything to do with the shoes I wouldn't have thought. Unless you didn't check them often enough, and the spring on the worn carbon shoe started eating away at the bell and ultimately toasted it ?? That would be a bit naughty Mr Malik