stability is the same on big and small quads (because you change the PID according to it's size)
small quads may have more agillity
bigger quads may can fly more smoothly
the exception proves the rule
Exact distances for official ArduCopters are 60cm Shaft-to-Shaft with longer 28cm arms and 46.5cm S-t-S with shorter 21.5cm arms.
Empty weight for 60cm ArduCopter without receiver or battery is 775gr. Receivers are usually 12-20gr each. Batteries (usable) starting from 150-180gr and up.