Happy New Year to you too!
You are pretty much the same dim's as me - 183cm/78kg after Xmas 🤶:-)
We find the best position for allround sailing is:
Front strap, second insert from the front.
Back strap, second insert from the back - so option 3 above.
Mast track slightly back from centre if you want tighter turning, centre for best control! good luck! Been loving the 81 out here in Cape Town, wished I had the 93 with me a few times for more float though too...and the 76 was awesome a few days ago with 3.7! :-)