Any ideas on the lowest profile open face , legal helmets? Any ideas where to purchase in Sydney? 

Have a look at nex brand open face helmets. Don't suit/fit my shaped head as some will/won't but I checked them out a while ago and they're low and Aust standards endorsed.

E-Bay also has heaps of helmets. I was thinking of a Half Shell Helmet for the reason Far Canal mentioned. My Open Face has massive padding making the front face on the sides stick out and act like air dams causing buffeting.