Hi Joe,
The consultants and midwives around you seem to be scaring you.
I used to be a midwife and, like you, I am big. When I had my baby I knew from around the last 6 weeks or so that he was big. His head never engaged (not compulsory but unusual for a first baby) and my midwife colleagues now tell me that they "always knew you'd have a section as you never walked like a heavily pregnant woman"!
The key thing with a large baby is how labour progresses. Scans can tell big babies but they are notoriously inaccurate at predicting the weight. I've seen many instances where they've been very wrong.
If your baby's head engages then that is a good sign that he/she will fit through the pelvis. I feel that sometimes the problems which occur in labour with large babies are due to the professionals interfering and adding drips to "speed labour along" and forcing an overlarge baby through the pelvis whose shoulders promptly get stuck at delivery. (Very rare thank goodness).
In your case - they know the baby is big so this should not happen. What they should do is give you a trial of labour to see what happens. If it doesn't seem as though the labour is going to progress (for example, the baby's head not showing signs of heading downwards) then they need to abandon that way of delivery and deliver him/her another way. ( if not through the door then through the ceiling ).
In my case it became apparent that after three attempts to incduce me all was not going to be straightforward. They actually offered me the choice of having an epidural just so they could break my waters (I wasn't far enough dilated for it to be a simple process) or calling it a day and having a section. After time to think I decided on a section - my ds was 9lb 6oz - I was glad I'd made that choice.
On the other hand I've cared for women warned of "big babies" who've sailed through labour and birthed their babies with no problems at all - the biggest I ever helped a mum deliver was 12lb 1oz!!!! . Don't know who was more shocked Mum or me. And yes, he was absolutely fine as was Mum - if a little shocked.
HTH a bit
Mandy