In our sports nutrition class, we used the text (Sports Nutrition – A Practice Manual for Professionals 4E) that was basically a collection of review papers and meta-analyses. We looked at two papers that came to the conclusion that 1.39 and 1.41 grams of protein per kilogram of body weight is probably the most that a 100 kg lean male atlete (basically a bodybuilder) would need to take in to satisfy their protein requirements.

Here's a quote from page 223:

Scientific evidence indicates that protein levels more than 1.7 to 1.8 g/kg result in oxidation of the excess amino acids (28). In other words, a higher than recommended protein intake does not result in greater muscle gain, even with an intense resistance training program. Therefore, it is important to increase both dietary carbohydrates and protein as well as consume an adequate amount of fat to create an energy excess.