Most FAI free flight sailplanes (F1A, F1B, F1H... ) these days use a flat center panel with raised tips. Dihedral at the tips is usually 15-20 degrees.

I think one reason polyhedral is thought to be more "efficient" than dihedral is that the angle at each break will be smaller, so the added turbulence should be less. However, there are more breaks... so who knows. I have seen several models with 3 or more polyhedral "breaks," although I have never bothered to build one like that.

My F1B model box is built to fit a single break at 15deg, so they all get built that way.

Personally, I think a single break at the fuselage looks ugly. I much prefer a flat center section or a 3-break wing.

-David