Our Proteus engines were limited to 11,775 CRPM on T/O, with the F/E getting those last 5 crpm manually.
As an "interested pilot" I was invited, on my own, to visit the people concerned. They were able to assure me that we "always flew at I.S.A." . They appeared to have no other information.
( Or did we not understand one another ? Sometimes it WAS hot, and sometimes it was cold... Was there a difference ? Could we use a higher cruising CRPM sooner when it was cold ?) Perhaps I was asking too much !