I have no probs wave sailing with larger sails in small, light to moderate conditions e.g. below = 5.9Volt on 100 @ 12-15kt.

Have had various 5.9 Norths, currently got a 5.7 Blade as my biggie. Tend to use them to stay on the water in 12-25kt bump and jump conditions. 5.7 on my 107 reactor is a really nice combo, tried a mates 6.3 Freek on the 107 the other day & it was surprisingly comfortable going back and forth.
My biggest consideration for using large wave sails isn't handling for chucking buckets or early planing, it's whats going to happen when I inevitably take a hit. In my mind... flopping around in a break with very little wind and rips that scream towards the point of no return, anything over 5.3 seems near impossible to get out of the water.
Once there is any size or reasonable punch to the wave, I'm in the 'big board+5.3 camp' for float & ride.