Doldrugs, certainly you don't mean splitting a 13lb dose between 2 people.?
And despite the variability problem, this 'experiment' could be very useful. As far as I can tell, if an A/B on the remains yielded little/no alkaloids and the product of the IPA was found to be decently active, you could deduce that the IPA extraction had a very high yield. Anyone agree?
Alternatively (and more complexly), one could use one batch of powdered cactus that had been sufficiently mixed to be considered homogeneous. One could then perform an IPA extraction on one half, an A/B on the other, then A/B the remains from the IPA and compare the alkaloid weight of the two A/B extractions. This method makes a few assumptions that would need to be worked through.