That is a really good question, about the 85 cm mast
Strapless in small waves or no waves/chop, I find my 83 cm mast totally useless.
But my 91,5 cm I use a lot in everything when a bit light in particular, and the 100 mostly when windy and tougher conditions/waves so to speak.
For me 85 would be an absolutely no go, but very different opinions it seems.
I use the same wing sizes as you are considering DRAZ99, 800 and 1200 cm2.
jumptheshark is probably spot on, impossible for you to know, you might love the short 85 mast, or you might hate it - impossible to know with so many different experiences