My experiences are similar to Jango's.
I worked on Garretts in Dornier aircraft in Oman and suffered temp limiting problems during the hot months. There is the possibility that both Jango and I are speaking about the same aeroplane and the engines on that particular machine were probably a bit tired.
I worked on twin Otters and Kingair 200's in Nigeria and had no problems with temperature at all.
Not sure how the larger PT6 types like the -65 as fitted to the Shorts 360 would cope though.