Can't recall which airline it was (OZ I'm sure), but on one info sheet they said you must "be able to comfortably walk down the aircraft aisle without having to turn sideways"
So I guess as long as you can do that then you're okay.
(I just wonder "comfortably" for who? Coz I wouldn't want a CC's butt hitting me in the face as s/he walks by!
)
I guess as with all things moderation is needed. If the CC can perform his/her duties without posing any risk during an emergency (as was mentioned about fitting thru overwing exits), and won't interfere with pax comfort (no hitting pax with your hiney, please...) then I don't see why they shouldn't be able to be a (healthy) size bigger than the norm (we don't need stick insects thanks) - and before you lash me, I'm one of the "stick insects" who would rather be a bit heavier, coz then I'd actually have more of a chance of getting work as crew- they look at me and think "She's so tiny - how could she lift
anything?
Sky