4300 is plenty for now. Gotta leave ourselves some room to grow later. Much later. Because there's plenty of other things we'd probably want before pushing for a bit more cargo.
It is kind of a shame the Large Train never gets used, but the thing should've been 4k to fit the Sirian Civ transport pattern to begin with. 1k, 2k, 3k, 5k... 4.5k? the hell's that about? But I digress.