The summary of research with athletes in the third source, which is fully cited shows that most athletes are in nitrogen balance with about 1 gram per kilo, or 90 grams for a 200 pound athlete. Some are not.
.7 grams per pound puts 90% of athletes in nitrogen balance. This would be 140 grams for a 200 pound athlete.
.85 grams per pound (or in another source cited there, 25% above nitrogen balance) produces the maximum amount of new protein synthesis, IOW protein synthesis does not go higher at more than about 170 grams for the 200 pound athlete.
100% of protein converts to toxic ammonia above 230 grams per day, or 1 gram per pound in another cited source.
ONE russian research study showed that over a 6 month period, athletes consuming 1.7 grams per pound were able to gain slightly more muscle over a 1 year period than athletes consuming .85 grams per pound. This would be the equivalent of the 200 pound athlete going from 170 to 340 grams of protein, but the did not test any intermediate level between .85 and 1.7 grams per pound BW so it is wholly possible that all of the marginal gains occured before reaching the 1 gram per pound or 230 gram per day level.
Also since ALL added protein converts to ammonia above 230 grams a day or 1 gram per pound, there can not be additional nitrogen retention at that point because all of the nitrogen is excreted. So the LIMIT of plausible added benefits and definite harms is 1 gram per pound.
That still leaves the door open to the possibility that more protein above that level would supplement glucose (it has to all turn to glucose when its yielding ammonia of course), and supplementing glucose may cause fuller glycogen stores, or more daily insulin production, but since it must yield a toxin (ammonia) it is less beneficial than simply adding glucose polymers that would not have the toxic byproduct.
I need to find one more, the study that shows that high protein can lead to insulin resistance…