Bard and I have raced the Stealth F16 in the last 2 sundays (6 races in total) in lightish winds and were sailing at about 165 kg combined. With us getting better on the boat we are making progress in placings (in a 40 boat strong F18/F16/FX-one fleet with typically 30 to 35 boats starting each race (so ex DNC's)) Our placings in order are : 23rd , 22nd, 17th, 44th (OCS darn !), 15th, 11th. It would appear that we are making steady progress towards the front of the fleet.
Just get your mind over that mental barrier and just sail fast and try to improof handling and feel of the boat all the time. Don't hook yourself on thinking that your weight is holding you back or something.
Wouter