You would get the top end out of the 7m but the 5.5 would probably be mor what you are after for surf in high winds even when these kites are in the top end you can still park them hit the brakes and ride at a comforlable speed. i ride my surfboard and 8m dos in 14kts so you should be fine on the 5.5m in 20 to 45 all reports back on the 5.5 say they are great surf kites stable and fast when you need them to be.