I am assuming that builders get the round cowl because of the nostalgic look. And the fast cowl to get a little better aerodynamics.
How much difference does the fast cowl make over the round cowl in max. cruise speed?
Are there other pros and cons for each of the cowls, say on a model 4 and/or Model 5 using Rotax 912ULS.
I tried searching this, but didn't find anything.

Thanks Gary