Thanks Rémi for your answer.
I understand that there is difference in shape and that the size has been changed for that reason. I wonder what will happen,if i change the vin size to 54 f.e.(for iSonic model 2006)
At this moment I use an 50 cm Tecnotronic for my 9.8 V8 N.P. When i am "finriding', i change it for an 48 cm Drake.If the wind then increases more i rig my 8.0 V8 . Sometimes i change the 48 for the 44 Drake for more control. And sometimes if the wind is not constant enough i let the 44cm fin and i change for an 7.0 V8 .If the wind still increase i use my iSonic 105l(model 2006) The reason for my question was that in this season i have a lot of more pleasure with my bigger sails and board so I hope that you can tell me if i have to change some thinks to have even more fun.