i thought you already had a pretty nice technical camera..
clearly the length of the bellows will determine the max magnification for a particular focal length.. to answer your question.
to be honest you are better off with a microscope objective past 2x.
I don't go above macro, and seldom even do 1:1. I like "context" and close-up is where I enjoy it most. I do have the large X-Act 2 Rollei Camera, but it weighs something like 14+ lbs without lens and camera. This is heavy and awkward to take out in the field.
The Cambo Actus is neat, small, and flexible enough for my work. I am also getting a Novflex BALPRO system because it can use the PROSHIFT adapter to take small panoramas, and supports many more cameras than the Cambo.
I agree, I am all set when it comes to Tilt/Shift. I like the "movements" a lot. I used to read all these technical articles about using tilt, etc., measure this, and calculate that. It was too complicated. Then I just starting looking through the lens and doing the tilt, shift, etc., and it was simple. Get it to where my eyes like it. Especially for a focus stacker, tilt can save many dozens of layers, etc.