To get planning with 5 mē, sail in only 13 kn wind, sounds fantastic even with light weight of 67 kg. Normally, with 67 kg, you need 15 to 16 kn wind for that and according to sail calculator you need 18 kn wind to get comfortably at plane.
We would all love to use 5 mē sail and get planning in 13kn, but reality is different. For me main goal for windsurfing is planning 100% of the time. My weight is 90kg, with 5 mē sail and 94l board I need at least 24 kn wind to get planning, if wind drops below 20 kn for 15 s, I go down.
With bigger board and sail 9.5mē I can get planning in 11 to 12 kn wind, for 7.8 mē I need 14 kn and for 6 mē 19 kn.
I try to choose my sail big enough to plane most of the time, but still small enough to keep control in wind gusts. This is important since there is no such thing as steady wind. Usually, if average wind is 15kn, there are wind gusts over 20kn for 5 to 10 s and wind lulls around 10kn for 15 to 30 s.
Generally, I prefer to sail overpowered for 10s every few minutes, than schlogging for few minutes and then get planning for 10 sec.
If I have to sail more upwind or downwind I tend to use bigger sail so I can reach much better angles of sailing. I experimented with sail setting below recommended min setting and could get planning with less wind. But then the batten tension was too high and one batten was broken.
New sails have much bigger wind range than old sails. It was harder to control my old 8mē sail in 20kn than new 9.5mē, so there is no need to be afraid from big sails, except for the price.