Hi Marc, depending on particular formula board, you can ride it with smaller fin/rig in comfort,
on older shapes I use to drop to 52cm+6.4m2 on really windy days for fun riding,
newer shapes like more power, so the smallest I use now is 56 cm (if I don't want to point)
and 7.6 m2 race sail (I think 8.3m2 would've being better). Newer race rigs and FW boards
have an amazing range and you can take it in open ocean conditions with some experience,
could be a bit scary in the begining but you will outgrow it. I'm light, so for a guy
your size in good physical shape, I wouldn't go lower than 8.5-9.0 m2 and 58-60cm fin,
and for your avg. day of sailing you want something in 11m2 range.