Yes but flat water (and wind) equals speed so even the fastest guy in QLD sails from Manly to Wello bank or Lota for the best numbers. All that part in the middle is plain old good fun but the numbers don't lie. The OP is asking for Speed Locations and from where he launches the closest is Wello and Lota for flat water.
Ilke - I suggest having a look on
www.ka72.com/ and you can type in locations to see speeds and people's tracks. This gives a good insight to where people are achieving their numbers. This combined with GPSTC shows who's quick and where.
It's also good to note what Mark is trying to point out if you can handle your gear with good speed in rougher conditions when heading to some smoother water it will only make your numbers better. Some of the fastest guys in Australia all sail in the bay (Manly/Wello) so just stick with them and ask for pointers if required.
Cheers
Marty