Gary,
My main halyard winch is an Arco 2 speed 30:1 self tailer
I needed it when I had a single sail of 54 sq m, but it's rather a luxury now, with a mainsail of something around 35 sq m. (3:1 halyard in both cases)
As David says, it's a great boon to have enough power to shake out reefs, particularly when sailing downwind in a big sea, left over from the big wind for which you reefed. You really don't want to round up to take the wind out of the sail, in those conditions, if you can avoid it. But I would think that a 20:1ST Arco winch would give you enough power for a 30 sq m sail. These are excellent winches, and since you are in Australia, worth having a look at.