Not really Kurt. Buzzard's points are all dead on. I'm not sure what you're referring to with your "apples and oranges" comment as it pertains to the portion you quoted.

Onewasp, not all sailplanes are good at punching out to get back upwind. Fly a Gentle Lady on a blustery day and you'll learn the meaning of fear And while it is a delight to fly in calmer conditions it has met it's match once the wind comes up. And due to the design choices in a model such as the Gentle Lady it will not respond well to ballasting other than maybe just a little to gain just a little. The airfoil and overall design just has too much drag to do well in a high speed mode. To see the gains from ballasting the airframe has to be clean enough and the airfoil one that works with low drag at very low lift coefficients or you don't gain at all or can even lose a lot like with the Gentle Lady.

With power planes such as flat bottom wing trainers this shows up as well. When you pick up speed you actually end up trying to fly the airfoil with a strongly negative angle of attack. It's still producing positive lift due to the camber but it's now running with a far higher drag coefficient than when it's flying with a neutral or sligtly positive angle of attack. When you compare this to a sport model with a symetrical airfoil the wing is actually producing less drag at high speeds such as when you firewall the throttle and then go into a slight dive to regain ground from downwind.

What you're seeing with a power model is not "penetration" due to the mass of the model but rather the difference in maximum attainable airspeed in level flight or at a reasonable descent angle due to the design. This maximum attainable airspeed
is actually what you're seeing as penetration on windy days.