I think I've said this before though. I have a hard time believing that only a few percentage points at the very top end of a pure product would actually make such a difference in the effects of the chemical- (What did Gale say about Heisenburg's concoction's purity? 97 percent or something like that?) Where Gale couldn't manage to get above 95?? I can't see meth purity turning it into something completely different - as Gus describes when he sought support from the Mexican cartel. Beyond that, anything that pure is bound to be stepped on at least once or twice so down the line it the potency would have been leveled to the quality of all of the rest and the guys at the top would have pocketed the difference, most users not even noticing.
but, I don't know if Gilligan had many advisors who were ever in the trade at multiple levels of distributorship.