Will Brink has some good info on this. Look for "The Whey It Is". Also Lyle Mcdonalds Protein articles.
Now I have, of course noticed some difference with really cheap econo whey concnetrates, as I'm sure everyone has. But I'm talking just making me a little burpy
. I usually like to have at least a mix for post because around the workout you are a little more sensitive to stuff....that's up the the individual of course. In the long run it's about comfort. If it hurts your stomach then that's a problem so you want something a little more filtered.
But through the years I've done it all and to be honest I've just never really noticed a difference except for the above mentioned.
When it comes to absorption rates if you compare whey to any other protein it is like comparing a Ferrari to a Ford Pinto. I mean, it's a Ferrari. You need a faster Ferrari?
If I use a really good micro filtered isolate around a workout for instance, I do feel like, wow, that's really clean and light. But that is about as far as it goes. It's not like a week later or a month later I've packed on even 2 extra pounds of muslce or I've gained more strength that I had with a mix or anything else.
I know many will say the opposite. Course you may want to look at their supplement list and ask how they can differentiate the effects of the 20,000+ things they take