At which linear speed should I do my turn motion relative to other motions?

As a general rule, the linear velocity of your turn motions should not be greater than the fastest of your motion, nor lesser than the slowest one.
It also seems logical that the turn motions are closer to the slowest motion, as you are supposed to slow down when you turn.
In extreme cases (when the slowest and fastest motions are really far), you will not get a vertical line separating your triangles.
This is a really bad configuration because it means that the blend of motions to get a "go straight motion" will mainly be done between two turn motions.
In this case, you will need to add a straight motion around the same linear speed as your turn motions in order to enhance the model.