How Many Horses does your Posi eat?

A drag racing buddy of mine once told me, that he had considered using a Dana rear end, but that it used too much H. P. compared to what he had. He said if his breaks down, he would rather keep fixing it than use a Dana.
I'm trying to set up my Duster's 8 3/4 and was thinking, what about all these Posi units on the market. Is there much difference in the H. P. loss comparing the Sure-Grip to the the Detroit True Trac, Detroit Soft Locker, Powertrax Lock-Right, Etc. ? How many Horses do these things eat and are they it worth it ?