I went to Bullen Merri today and it seemed like it could be an ok spot if you're more experienced. I'm really just a beginner and on the south side of the lake where there's more of a beach, the wind was all over the place today, hitting me in the face one moment, then from behind the next. On the northern side it was really choppy, but the wind was a more consistent sideshore (still a bit unpredictable), however there was only a very small section of beach where I launched and I was concerned about being blown too far along and hitting the rocky shoreline. Considering how insanely deep the lake is (66 metres) and how quickly the lake bed drops beneath your feet, I didn't really have the guts to venture very far from the shoreline before turning back, so couldn't really appreciate it. I also stubbed my toes numerous times on rocks. I will go back here for sure once I have more experience to know I can get back safely.
I think your assessment that it would be best in a northerly (or something with a bit of N in it) is right. That south beach is the best place, both because of the width of the sandy beach and the fact there's a nice big grassy area to rig.
The water looks really clean and the lake bed is sandy too. It's brackish, so while it tastes salty, it doesn't leave you feeling quite as crusty as the sea once you dry off.
I knew Bullen Merri was deep, but wasn't quite prepared for the bed to fall off quite as steeply as it does! You walk in and 5-10m from the shore you just feel it plummet beneath your feet!
Is Port Fairy a surf beach, or is it relatively flat? Flat is the main thing I'm looking for at the moment. Think I'll stick to the Mornington Peninsula on anything with a some west and not too much south for now :)