Hi Col,
I know of at least one IIS member who bought a 12" a few years ago and wished he'd gone 10" instead for easier handling, but that was undoubtedly based on dismantling and transporting the scope to dark sites. If you're gonna use it at home on a trolley I say go for the bigger one.
I also agree with Martin's comments (except I don't know why his 10" Dob could only resolve 4 stars in the Trap when I can see 6 in my C5
).