I'd sail the SC 20 solo til 10 or 12 knots of wind. Then there wasn't enough ballast aboard to deal with the power. Consider reef points on the main(good for family sailing as well), and/or a smaller main, and a furling jib(to reduce sail). I really liked the additional buoyancy of the 20' hulls(vs the TheMightyHobie18 Mag) when it came to more weight on board than the conditions might be calling for. Sinking the hulls on the 18 really slowed it down. The biggest downside fo the bigger boats is more weight.

Dave