You're going to be struggling quite often at 85kg with a 85 RWW on Botany Bay. Fine when it's blowing well, but there are many marginal days in Sydney. Either you only go out when the wind comes in good, or plan on getting a 2nd board, (maybe 110 litres?) for those other days.
Most who sail Sydney will have at least two boards to maximise the chance of getting out on the water.
Oops, just noticed the John Hall you got. It might fit the bill for light wind nicely.

(Although the rails look mighty square.)