When you talk about quality - do you mean in terms of % of Ethanol? The biggest risk I see worry about is that it gets too much moisture in it which is why I like a place that sells a lot of it. For a street car running E85, it should have the flex sensor, and it won't really care if you get 51% or 85%. In fact, at 51% you are probably getting a better deal for a regular car since you are getting more gasoline at a cheaper price.
But yea, if you are running a boosted car without a flex sensor, you could run into some real trouble if you are tuned to 85% and you get 51%. I think at that point I would probably be buying it by the barrel too.
-Geoff