If someone tests in the wind tunnel on "one side" of the curve and rides in the same regime, then their results are likely to be very close, but if not, they can differ significantly.
One other thing that most people forget when thinking about "sailing" in the wind is that gusts that change the yaw angle significantly can cause flow separation that remains even after the gusts go away due to flow separation hysteresis. Basically you can not have separation at say 15 degrees at first, but if a gust comes and changes the angle to 20 degrees and causes separation, the separation bubble will remain even after returning to 15 degrees. This may be why in the real-world people don't experience significant sailing and why real-world results *can* be very different then what is experienced in the tunnel. And for most wings, this effect is around 12-15 degrees (lift on top, drag on bottom):
For the smooth vs rough, I understand what you are trying to say, but the effect is also strongly a function of the nature of the roughness, and placement of the trip wire.
For a point of reference, a 2 inch (25.4cm) diameter sphere in a cross-flow of 40 kph wind, would correspond to a Reynolds number of about 40,000 (hope my math is right). This is the onset of drag crisis (big drop in drag) for a dimpled sphere. I agree 100% with the hysteresis. It is certainly overlooked, but for low Reynolds number cases doesn't it rely on the flow actually being laminar at the separation point? This is something that would depend largely on the nature of the incoming flow and surface roughness too.