I have been shooting with the 7D since it was released and now I am thinking of moving to a FF. From what I gather the 5D MII was a stellar camera and in may ways it still is. The question I want to ask... if the Mark III is an upgrade to the features that were lacking on the Mark II shouldn't it preform better?
I have the 5D Mark II, but I got it for shallow depth of field, and better image quality at mid to high ISO. For this, full frame DSLRs excel APS-C cameras, it's really no contest.
However, for macro shooting and landscape more depth of field is desirable.
Also, I take it that you are likely to be shooting at ISO 100 ? Here it doesn't seem nearly as clear to me (but maybe someone who knows more about landscape/macro photography than I do which is a low bar, can help add some clarity to the discussion). Some of the better APS-C sensors outperform full frame sensors at lower ISO (e.g. Nikon's latest APS-C cameras have more dynamic range at low ISO than the 5D Mark II, though the 5D wins hands down at higher ISO)