For me, p4p is: you give a fighter a certain specific level of how good of a fighter (open weight wise) he is, and then divide that with his fighting weight. (Simply: the fighter divided by his own weight). It's by far the most mathematical approach and it would tell us literally how good a fighter is pond for pound (since the answer would be of the unit "fighting skill/strength per pound")
Problem is, it would be very hard to give a fighter a numerical rating, thus making this approach ungainly. It would, however, be the best way logially speaking.
I say can't we just say that we have an unranked top 5 (i.e. the estimated 5 best p4p fighters with no ranking between them), and the same with the number 6-10 p4p fighters. Cuse most of us think that Anderson, GSP, Fedor, BJ Penn belong in the top 5. We only argue aout where to rank them. So wouldn't it be better not to compare them to eachother? We would save a LOT of discussion time that way. (p4p arguments are starting to tire me out