i went from my ALLWAVE 9´6¨ 170 liters (by that time 105 kg) to my actual hokua 9´5¨ 140 liters (loss 30 kg also, now 75-80)
It was very doable and the hokua was a game changer, excellent surf board!!! Now dropping again to the Hypernut 105 liters (have to wait till september to a review)
I think that 140 liters and the 9´5 hokua is an excellent choice for "surfability", stability and comfort in choppy windy days. That board cand handle big waves (3 meters faces, at least big for me) with 12 second periods, easily.
It´s forgiving, has good glide and is a wave catching machine.
If you are going to drop, 30-40 liters is a good number, anything less than that and you will want to go smaller in a few sessions.
my recomendation..push your limits a Little more.
20 liters in 190/170 and you will not feel the difference. Go a Little more smaller. 140/150

YES YOU CAN!!