What board(s) do you have that cover 13 to 30 knots? Hard to believe that at 67 kg, you can hang on to a 5.0 in 30 knots. Occasional gusts - yes. Steady 30 - no way without luffing all the time.
I guess I am one of those "macho" guys since I would use a 11.0 in 13 knots and a 4.0 in 30 knots. I weigh 78 kg.
In between I have - 9.2, 8.4, 7.6, 6.6, 5.7, 5.0, 4.5. Some of these (smaller ones) are quite old and don't get much use so they last a long time.
Also, at 13 knots of wind, I am traveling at 24-26 knots of board speed (gps speeds) on my formula board and 11.0. I doubt you can match that performance with a 5.0.
I do have a light weight buddy about your size that covers a very broad range of wind (10 - 30 knots) with a 6.5, 5.7, 4.5 & 3.8. He also uses three board in this range. One sail simply won't provide the appropriate power in 13 - 30 knots. You have to sacrafice too much at both ends of the range.