[Christ]

I've always pumped at the first auto-click in the handle, only to prevent loss of fuel from splashing and overflow.

The actual issue with pumping quickly (whether it's true or not, I suspect not) is not foaming, it's vaporization. The idea is that the faster you pump your gas, the more quickly it vaporizes, and the more of it you lose due to evaporation.

The idea is probably somewhat correct, but the time differential sets it off - If you take longer to pump, even though you're creating less vaporizing turbulence, you're giving the fuel more time to vent into open air.

If you pump faster, you're creating more fuel turbulence, which might vaporize more fuel, but you're giving the bulk of the fuel less air-time to vent.

It's probably a wash.

The other issue is that fuel pumps are certified with a margin of error, maybe +/- 1%... the pump is more likely to "break even" at a slower speed.

When you pump from a preset, most pumps now slow down when you get within about 1/2 gallon of that preset amount, so they don't cut off too soon or go over. Keeps you closer to being "on the dot".