I'm 5'10" with a 32" inseam. I got a medium and it comes below my knees. Even with your extra 1" in height (could be legs, could be torso), I think the medium would be plenty long.
Edit: also check out the cuben "CloudKilt" from ZPacks/traildesigns. Costs more but weighs a little less. There are a few pictures there that might be worth looking at to gauge size.