Well, if the output from devel/watch-minecarts is correct for speed, then I'm certain that minecart + 2 nestboxes is treated as 25 Urists, not 25,2 Urists as it should be.

Your odd water plant would still have required figuring out cycle length. Granted, once that is done it is convenient, I suppose....

Wiki would have static table, which isn't very attractive, as you'd need a separate table for each possible cycle length (ranging from 1 to 50000) to display the array of suitable weight min and max multipliers for each input speed and friction.

But as far as quick guesses go, a quick and reasonably accurate estimate for single-step movement cycles can be gotten simply with input speed*input cart weight/((50000/(cycle length-0,5)+suitable friction).

Ex, 200 repeat cycle, normal wood cart, 2174 input, medium friction: 24*2174/(500+50000/(200-0,5))=69,5. Toss into cart 2 doors, bin and bucket for 50000/(2174*24/70-500) = 205 repeat cycle. Or leave out bucket for 196 one. If you leave out the -0,5 part and have a convenient input speed, could calc it entirely in your head quickly.

Can obviously get closer or exactly to desired results with lower frictions, higher weight carts (here in particular, tossing another cart into pusher cart is attractive) and multiple movements per push (the formula for that one is kind of complicated), but just to show that it can be pretty quick to calc.