Seriously, do you realize how stupid it sounds to argue that you get more leg drive during a stiff leg deadlift than during a conventional deadlift? That's one of the most retarded things I've ever heard. You don't get more drive by keeping the knee joint from moving. You seem to be inexlicably, somehow, retardedly equating "leg drive" with "tension on the hamstrings" for some reason.
I guess that's why the world record for stiff leg deads is significantly higher than conventional deads. Oh wait, it's the other way around, as you would expect, seeing as how conventional deads get more leg drive than stiff leg.