[consp]

If you take this measurement as the goal it would be best at near standstill speed (around 4m/s). If you want to maximize the traveled distance of the group it is around 60kph, which is the metric most people actually care about when discussing throughput.

[CGMthrowaway]

1 car / (actual max following time) no matter the speed. Where do you see speed in the equation? It's not. You can put it in of course but my point is it's unnecessary if you know following distance, which is theoretically more invariable than speed on a road anyway