Thanks so much for your high value advice.
Here we have two diferents point of view: my friend and mine.
After sailed the bigger Fut155 with 6,5m sail (im over 80 kg) i see Fut can handle more wind than initially expected. Thats why i will go bigger/ confortable.
But my friend is ligther, skilled and whish better control in HW... maybe with big rig/fin and good pump skill he would plane early in LW.
Regards and thanks a again for your help.