Diameter or length?
I would be using minimum 3.5mm and order/buy 1m (3'3"and 3/8 for you lot) per saw.
May not take the full meter to fill the pulley, but it allows for knots and mistakes if you have a bit of extra length.
Original spec for the 2077 was 3.8-4.2mm and 965-975mm length- same for 2094, so guessing it was the same for the 2083.
So I said 3.5mm minimum (if you use proper good quality recoil cord) and if you want to play to original spec- use 4mm.