hi WD.
There are quite a few sailors around the 70kg weight who are doing okay with 100litre boards and 5.7m sails as "their big gear"
IMHO - Unless you intend to use the board with a sail larger than 7m and wish to sail on very light wind days, I'd say you could easily move to boards 90 - 110 litres. You sound like your past the need for very floaty boards.