Trying to get within a mm or two without actually trying the set up is a big expectation. The reality is that how the arm fits the taper, how close to "perfect" dimensions the bike's BB drive side from frame centerline is, where along the BB shell does the chainstay reside, how the chainstay is indented (or not) are all variables that one has a very hard time really nailing down without actually trying a set up. When in doubt go for more stay/ring clearance.

This is one of the situations that working with your LBS can make things go far quicker. Andy