That range is from 120-140 (funny enough, same 20 lb range you have). Alhough I wear a 12 when I am 140, it is mostly b/c I like my clothes to be loose fitting and comfortable--I like room to breathe.
I am most comfortable at 130. I look too fat at 140 (where I currently am) and too old at 120 (not enough flesh on my face). Although I am not unhealthy at 140 per normal standards, it is considered unhealthy for me for medical considerations. My doc warned me to get back down to 130, and I need to do so.