I have a 20F Incubator under quilt and am looking to get a top quilt too. I'm a warm sleeper (usually like it a little cold) and am thinking that I could get by with a 40F top quilt for the shoulder seasons (when temps might dip into the 20s at night).

My main concern is actually on the hotter days. If temps are in the 50s, will a 20F under quilt and a 40F top quilt be too much? My thought is that it is much easier to regulate a top quilt so this combination should be OK. Any thoughts or recommendations?

I'm curious about this too. I'm probably getting the Incubator 20 and I'll be coupling it with my Marmot Helium 15* sleeping bag as a top quilt. I have a hunch it's going to be overkill for my August trip but I know it gets into the 40s/50s so maybe I'm over thinking it.

I think you'll be fine in the warmer months. Just wear less, stick your feet out and cover up what you feel like at the moment. I've brought my 10 degree down mummy bag on all trips since 1983. I now use it as my topquilt.