we have lift off
I would say that it would be quicker to use a banshee for taxi missions with no collecting of cars for import export. If you just have the taxi missions to focus on I think you could do it in 1 segment. This would require careful collection of cars for import/export but there is clearly no difference between picking up cars in between missions for import/export and doing it in taxi missions. So as I see it, you would overall save as much time as is quicker to perform taxi missions in the banshee as opposed to the taxi car.