The Ever Given has a maximum speed of 23kt / 42km/h and carries 20,124 TEU or approx. 7660 54-ft containers.

Rail figures are harder to find, but a reasonable guess based on what I can find seems to be 400 containers per train if the loading gauge permits double stacking containers. Speeds over 100km/h are easily achievable on railways without at-grade crossings.

So one ship could easily require ten trains to move all its cargo in the same time, plus the time taken to offload at each end, which I guess is why this hasn't taken off. Though if it's all just transhipped to trains this could be faster than at most ports where containers have to be sorted to different destinations.

Though interestingly with a dedicated right-of-way the trains don't actually need to be manned, remote control freight trains exist.

I could foresee a parallel loading crane to train track system where the cranes take up to 10 or 20 containers at once and then put them on 10 to 20 parallel train track at once on the other side.

Hand counting how wide a panamax gets, they seem to max out at about 19 or 20 containers wide and 15 containers deep. It also looks like shipping containers already can be top latched with this video: https://www.youtube.com/watch?v=GZQPxl9zssk

So if you could automate this system at 30m per transfer of 10, a port with 15 cranes could do 300 containers an hour and clear a boat in about 15 hours. You could expand the system further into a full panamax width and do it in about 8 hours per panamax boat with 4500 TEUs.

In practice, the mean speed of a container on a ship is probably close to 10 knots. A freight car would be lucky to mean 5 km/h.

Freight trains run usually at 80-120km/h on railways with at-grade-crossings (for higher speeds you would need better brakes, and more energy which doesn't really make sense for freight). At least in Europe you only need to eliminate at-grade-crossings if you want to run trains over 160km/h

Doing 100 mph with a freight train is well possible, if the track can take it.

Though often you want to go slower for less air resistance.