Cornwalls and ATC/Dukes have diff signatures. test over 12 speakers a few years back including 20.7, etc and really only 4 gave me the sound that i was looking for (40.2 being the 4th).
ive heard the 20.7 - love the sounds stage and quickness but thats about it. Ive heard the Cornwalls - wow the lively sound. Heard that the lascalas lack bass.
for me in regards to the use of floor space, i would take floor stands over stand mounts with sub woofers. imo the later system takes more space and even more fine tuning to your room.