I can’t comment on the mod, but the best cruise altitude is variable and depends on a lot of things, such as Standard Atmosphere (ISA) for example. If you look at the TBM930 Pilot’s Information Manual sect 5.11, you see in the graph and subsequent tables that FL310 is acceptable at ISA -20, but FL280 is the logical max at ISA, before fuel flow and speed take a hit. At ISA + 20 you would need to cruise at a lot lower altitude.
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