Well today I went sailing on my F159/10.3 combo. The conditions were 5 to 15 knots, which to me means 30-50% non planing. Just for the fun of it I took out my old Mistral SLE 311 (not a real longboard and it doesn't have a dagger, anyway it's only 8 kgs).
The Mistral appeared to be a lot of fun in the light gusty winds. Due to the longer waterline it went at a noticeable higer speen than the formula when not planing. This speed again generated some more airflow around the sail which made it more powerfull and stable. The result was surprisingly early planing and way better schlogging. Non planing on a formula is pure waiting (waste) time. On the long(er) board it became quite fun. I have to admit that the Mistral had seriousely problems upwind compared to the formula and when the wind came up to a stable +10 knots the formula outperformed the Mistral on any point. Anyway 5-15 knot days are common 75% of the time in my area so, I really think that when the year is over a longboard will have given me the most pleasure....