Part load efficiency data is kind of hard to find.
But it stands to reason that it too will follow the basic trend of the Carnot efficiency equation of Nth= 1- (Tmin/Tmax)
Attached is results of an experiment of adding an intercooler to a turbocharged engine and keeping fueling the same.
and finally here is a link to a book on diesel engines. If you want to do a detailed analysis or partial analysis of how intake air temperature will effect things by plugging in numbers to equations this book will show you how.
http://www.dieselbookmarks.com/bombe...nce%20Book.zip
I can dig up some further studies and papers by NACA that show a similar trend if you like.
Edit: added the words "the same" after the word fueling