Above 7,340 FTAMSL with 28ºC many machines seem useless
Mmmh, these are not bad helicopters but altitude makes them sad and nearly useless useless machines.
I once heard a Bell Demo pilot say, "All our helicopters are really good until we bring them up to Mexico City" he said this after landing in a 430 at a pad we have which is at 8,000 with a usual DA of around 10,500, and realizing you could carry more people further in single 407 than in the twin 430, its a fact that many multimillon twin engined machines are outperformed by newer singles such as the 407.
The Bell 222 pilot on board and 45 minutes fuel was all you could use without having to roll for takeoff, then once airborne, if you make steep turns in the wrong direction, the TQ goes up like crazy and you could overtorque!? you could carry more in the 206A. The 230 is also very limited.
S-76, the ones I have seen up here could only depart an elevated pad with 3 on board (pilot included) with about 50 minutes fuel to tanks dry, again you could carry more in a 206A.
EC120 performance is ridiculous at this altitude for a newer generation machine.
Same for the MD600N, athough its nicely quiet.
Agusta 109, (all of them except the K2 and Power) takes real guts to depart an elevated pad with no wind around here, at any weight!
206 L4's are great but have a very dangerous characteristic at altitude, they will run out of pedal in a normal T.O. and have you spinning in a second, this is if you are near their limit or get the slightest wrong slde crosswind. (the ones with the Std. T.R.)
Could think of more.
And I know you mentioned only turbines, but I really dislike the R22, I can't belive they let them get away with those dangerous flight characteristics, especially when its flown mostly by new pilots.