Hi Mike,
I understand your logic on running the .043 gauge vs a .325 chain like LP, the difference in chains is substantial. I`m not convinced that the difference between .043 and .050 lo pro is enough to pull the saw out of it`s powerband, but then I`ve never run .043. I`m surmising that you run a Stihl pole pruner since I don`t think anyone else is running .043 are they? My Echo PPT-260 handles 91vs just fine and I can`t believe that the HT-75 wouldn`t. You might be surprised if you tried it. I`ve heard people complain about the .043 being so small that chip clearance is a big problem.
Russ