With my limited experience with 20" kick drums, I definitely prefer the sound of a 22" kick. They have more oomph and low end.
Some 20" kicks do not project quite as much as I'd like them to. It sounds like the volume knob on the kick is turned down a notch. (relative to the volume of the rest of the kit)
If you're playing quieter genres in small rooms, a 20" kick would be totally fine. But if you're competing with loud guitars, the 22" is definitely what you need. They just sound deeper and fuller.
For portability, the space savings between 20" and 22" are negligible for (most) small stages. Usually, it's the DEPTH of the kick that matters more on small stages.
As for a 13" rack tom, I'm not totally against it, but I prefer a 12" rack tom because they're "faster" and more punchy.
I have played hundreds (probably thousands) of gigs in small rooms with little to no miking...and I definitely see the benefit of an 18" or 20" kick drum in those situations. They definitely have their place. But I still think 22" is the magic number.