The figures in the links indicate that the 5 pole motors are slower revving with more torque and generally lower current consumption than 3 pole motors. Just what is wanted for a tug, and most other dispkaacement hulls. It is possible to have a different wind on a 3 pole motor to take it into 5 pole performance territory, and vice-versa, but it will always be a second best choice because of the underlying physics.
It is a sort of convention that a 540 is a 3 pole motor with a case length of 54mm, and a 545 is a 5 pole motor in the same size case. There is, sadly, nothing to stop any manufacturer ignoring the convention, and has probably happened. The recent trend by manufacturers of creating "new" series' of motors by rounding up (400s, 600's) does nothing to help cut the confusion, neither does the habit of some modellers of rounding down (300, 500 etc).