To Regis, @78 kg and my KOOL1200 wing, I use the 3 and 5 at their sweetspots where not flapping nor having to work, in wind around:
5 m2: 14 to 17 knots
3 m2: 20 to 23 knots
Using my WaveXL (790 cm2) windranges are not that much different, because of more apparent wind power as one rides faster, also in jibes.
Low end, below above sweetspots, are higher with the smaller wing though..
My 4 m2 on the way, believe it would be around 17 to 20 knots then, but dont know yet
Windrange are somewhat higher than these mentioned, have been riding the 5 m2 in more than 20 knots easily, and lulls at 11-12 knots same session, so when wind is very changing it can still be used.
If you rarely have waves Regis, I assume they are wind waves, thus a 4 m2 might be a good size?
Dont know if this helps, as I dont have as much experience as tomtom and drsurf, but might give an idea