[QUOTE=spclark;23604121]. . . On a trainer where there's no wind, or outdoors when climbing, what's the % between incremental miles per hour look like up to maybe 20?

Of course, most or all of the various software alternatives designed to control smart trainers are programmed to replicate the increase of resistance into the wind as closely as possible.

So you can answer your own question (at least the part pertaining to smart trainers) easily by noting the percentage change the next time you do an indoor ride.