I find ACEx or Swiwin turbines to be the best for high alt r/c fields, personally I think a lot has to do with how big the intake/ compressor area diameter is (bigger the better). Jonboy I knows we have flown 80, 120, 140, 170, 190 and 220 sized ACEx turbines and not one flame out, no hot start or any issues. I just think the front intake compressor area's especially in micro turbines is just too small for high alt flying. Maybe I am wrong but from my experience turbines with smaller front compressors over time end of having issues, especially during the hot summer and high altitudes and sometimes just not enough direct airflow into the intake and compressor. ... I'd love the mirco turbines but until one is proven to work at these alts, I won't buy one.