From some googling, average freight speed in the US is under 40km hour. And that includes huge stretches of track without a curve or a mole hill. The capacity limitations end up at the depots anyway so going faster just means hurry up and wait.
Systems are not comparable. US systems are to my knowledge: all above ground; long trains, which require longer stopping distances; require manual loading; coupling of trains is manual; driven by humans; distances traveled are completely different; one-way, single direction, per use; breakdown cannot be routed around; etc.
