LowNSlow - re Rotax RPMs, I can only speak for my Europa, which is fitted with a Rotax 914 and variable pitch prop. With the prop at its full coarse setting, it cruises at around 120kt at 4600rpm, or 100kt at 4000rpm. I tend to use somewhere roughly in the middle, but I would guess that your quote of "high 3,000 to low 4,000 for cruise settings" may be slightly on the low side compared to my experience, although not by much.
I don't know how this would compare to a Subaru engine/gearbox combination.
FFF
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