Dave - You're right that open class flew further but not by a lot: 575km averaged over the 12 days vs 534km in 18m class. Parity time-on-task would have the open class going 538km to the 18m 534km; the additional 37km puts them out 14.8 minutes longer. I'll agree that there would be a small effect from the open class having to bracket a longer soaring day; but the 15 minutes addition is not enough to make much difference and does not alter my own conclusion on the matter.