I have Armie ML85, and yday I tried the Midi 82L.
The Midi is shorter and thicker and off foil is way more unstable than the ML85 and a less efficient in taking off.. Then on foil, it's a fun board, I liked it. Not a light wind board in my opinion.
If you an intermediate rider, with Armstrong ML you could go -10L easy from your weight to find the right volume even in very light wind.
With the Midi I'd go @ your weight, cause the thickness of the board makes everything quite wobbly in light wind conditions.