wiper motor different speed

[nietolerancyjny]

This is my first post on this forum - Hello everybody!
At the begining sorry for my english, its not my native language.

I'm building 2dof wiper motor simulator based on RacingMat work (thank you!) simulator (2dof, wiper motor, arduino & motomonster).
I'm using 12V truck wiper motor from polish truck ("Star").

I perfmored some test, first of all i noticed that my motors spining one way faster than another (like 2:1).
I've opened the case and saw 2 wires and 3 brushes (1 brush -> negative to motor case) - so now i have 3 cables (1 for high speed 1 for low speed)
Brushesh on opposite way (low speed).
After this tweaks motors can change direction with the same speed (youpi!!!)

The question is: Should I use high speed or low speed?
Second question: I dont know why, but the one of the wiper motor is faster than 2nd about 20%. Do I need 2 identical motors with identical RPM (speed?) what can i do in my case? Do i have bought another one or it can be done by using a software (x-sim?)