Hi!
I have flown in the back on both. While the -900 IS better than the 50 seaters, the 170-195 is A LOT bigger inside, with bigger overhead bins. It is A LOT more comfortable for the pax.
I would assume if you're small in stature, the main advantage to the 170-195 is the wider seats and the bigger bins. The overall size of the aircraft wouldn't matter so much.
cliff
YIP