Not sure, but below 22 km/h is What I have heard

Going up the hills they were going as slow as 11km/h

Assume your CDA 0.2 in aero and .35 sitting up

Aero watts at that speed would be .5 * airdensity * cda * v^3 (assume no wind)

So at 11km/h

.5 * 1.18 * .2 * (11/3.6) = 3watts
.5 * 1.18 * .35 * (11/3.6) = 6watts

So if you can put out 10 watts more sitting up, you are still 7 watts ahead.

At 25km.h

.5 * 1.18 * .2 * (25/3.6) = 40watts
.5 * 1.18 * .35 * (25.3.6) = 69watts

So a 29 watts difference

So if you can produce 30watts sitting up, that is your break even point to sit up/

Theoretically :-)

That is truly amazing, thank you!