Sounds about right, or maybe a tad more... I was fitting through an
exterior rendered stud wall (which is a pain to make holes through
because it starts out with mortar, then expanded metal lath, then ply,
then foam, the plasterboard - try finding a drill bit to go through that!)

I held the end of the elbow against the wall and drew round it. Used a
chisel on the SDS to cut round the outside of the line, tin snipped
through the lath, then used a 5" hole saw on the ply and the
plasterboard and foam. I actually found the 5" hole in the ply was still
a little too small and needed to attack it with a reciprocating saw. So
I would guess a 6" hole would see you clear. It does not need to be that
size all the way through BTW, because the elbow will only penetrate a
couple of inches into the wall.

Sounds like fun! Well, I need to get through approximately 2ft of the
hardest brick in the world so I'm going to look into hiring some form of
diamond core drill - just to add to the fun I'll be 20ft up a ladder in gale
force winds at the time - woohoo!! :-|

Andy