Like was stated earlier, a person's own metabolic rate, body mass, etc... all contribute to a person's ability to metabolize and absorb protein. This does not just go for protein, but any nutrient.
I can't point you in the direction of hard evidence, but I am basing my opinion on medical studies, personal experience and the studies of nutritionists and personal trainers. I can attempt to dig up the hard evidence, but it will take some time. Anyway, I meant to address the question in my prior post, but I ran out of time. On average a person can only metabolize and absorb about 45 grams of protein in one sitting. Now with that being said, taking into account all the factors stated above, this number can reach as high as 60 grams of protein per sitting. It is extremely rare that someone could absorb more than 60 grams in a sitting, but while on a cycle, you body is able to absorb and metabolize more protein, and in turn your body needs more protein at each sitting. While using gear, that absorbtion increases, but it is still more beneficial to maintain a balance of protein intake throughout the day. When training people for weight gain, and even during weight reduction, I recommend waking up at around 2am and drinking a protein shake that contains atleast 40grams of protein. This is a good way to make sure your protein level is high enough, and also helps with muscle repair that is done while you sleep.
Sorry this is so long. In short, the average metabolization of protein is between 45 and 60 grams in one sitting, but while on gear, this number will increase.