I've done Lake Mac to Sydney a couple of times in my Top Hat solo. The last return leg from my log shows 40.5 NM from the courtesy bouy to my mooring in Careel Bay. Average speed was 5.4kts, and about 7 hours 30 mins. The Sydney leg is half that, depending on where you need to get to in the Harbour.
In my opinion, try to choose the last hour or so of the run in tide to make your way out the channel, its pretty fast, but easier to control not running into the bridge than with a run out tide. There is viirtually no slack water, the change there is pretty quick and about two and a half hors after the stated high or low tide due to the size and volume of the lake.
I had south easterlies last time that turned north later, made for good sailing, even though the swell was over 2 m.
Ramona is right, I reckon anything other than due south is pretty good winds for that trip, especially if there is west in it, it will make the seas really smooth and you'll just glide down with the dolphins.......
