Are 1-1 trains viable?

I know people tend to do 2 freight minimum to look more like a train - but on average, is the throughput of 2 1-1 trains the same as 1 1-2 train? Assuming traffic at intersections isn't an issue, I'm wondering if the saved space of one less freight car will cost me elsewhere.

I ask in part because - for example - I have a 1-2 train getting bauxite but both cars only get maybe 5-6 stacks in each before the train returns as the extraction rate isn't enough to fill even one car before a round trip.