Originally posted by s.wilding I still have access to the 5dii, so I'm starting to kinda build my "budget pro" system on the side.
If you meant you have a friend/associate with a 5DII, or that you plan to continue to rent it on occasion, then why not use another Canon body and lenses just so you can mix and match. And the controls and ergonomics should remain more familiar.
My comment has nothing to do with FF vs non-FF. Personally I feel DOF can easily be too shallow with APS-c so I don't see the need to make it thinner. And for studio portraits you will be shooting stopped down anyhow. Anyhow, maybe a 7D would fit the bill.
Don't get me wrong, I do happen to love my 18-135, use it 90% of the time and would easily recommend it for general purpose, but you're saying various things in your OP which seem to indicate needs are different from mine.