Have got the bug after an afternoon down Fistral on the weekend - loved it!

I'm looking to get an NSP mini mal that is 7'2" in length. I'm 5'7" tall and weigh 75kg/165lb.
Will this be too short? Should I go for a 7'6" instead? I've heard 1.5 - 2ft longer than your height is a good size to go for???
Cheers
Gaz