In order to further clarify the advantage of tapered bands, I re-watched the slomos done with Destin's camera.
I noticed that the elongation of the rubber close to the pouch was a lot higher than the factor 5,5 (which is the way the band was cut). It was more like 7.
So it seems possible that the extreme overstretching is responsible for the speed advantage, as that does not happen on untapered bands.
In order to test this, I made a stretching stick. I put on a 2cm wide strip of TB Gold and markered the 10 cm length point. Then I attached a hand grip, with a karabiner in order to draw with the scales.
The first interesting finding: TB Gold can be stretched to the factor 8! That is right. But the draw weight increases steeply between 7 and 8.
Second interesting finding: The relaxed length increased. After stretching it out to the 80 cm, the relaxed length was 12 cm instead of 10...
Of course there is hysteris, means, if you keep the rubber drawn out it looses power swiftly. But it recovers, and fast. After 10 minutes, the relaxed length was 11 cm.
Third finding: Stretching the rubber that far breaks it in, means, changes it forever. The rubber did not go back to 10 cm. It stayed at 11, even after a few hours.
Fourth finding. Once broken in (stretched out to 80 cm and held there a bit), the rubber permanently looses draw weight.
See the attached graph - after the break in, 80 cm draw can be achieved with the draw weight needed for just 70 cm in unbroken in condition.
What does this mean? Well, the next experiment must be to cut a much shorter and thinner band set than usual, without tapering, that can be stretched to factor 8. The chrony will tell what the effect will be.