I have 145 Tabou Rocket board. Sail range for this board is from 6.0 to 9.8. Does that mean that board is not designed for sails under 6.0? What will happen if I use sail 5.0 or 5.5 for stronger winds?

IF YOU USE THIS BOARD ON A 5.0 OR 5.5 YOU WILL EXPERIENCE A FEELING OF BEING OVERPOWERED. THE BOARD WILL HAVE A HARD TIME TRAKCKING STRAIGHT AND IT WON'T FEEL VERY BALANCED.