First off, not sure how it is at your GNC, but the three around here are not places you want to take advice from. My GNC recently fired a guy cause the manager told me that he got incentives for selling so much of certain brands (as in the brand name offers the employees of GNC these incentives). I haven't found anyone worth talking to there. My buddy works at Vitamin World and he told me that the info they give to people is basically scripted from the company (i.e. marketing crap).
Also, alot of the mass market brands are loaded with stuff you don't need (i.e. fillers and extra sweeteners and gum blends) and void of the stuff you do. Try to find a site that sells individual ingredients and mix what you want. I like PF, but there are others.
If you are talking about the pro series stuff for $55.00 for 5 lb with gold card then you could get a far better quality protein from PF for about the same price per 5 lb bag.