It seems clear we would like to have a Jake instead of a retarder, but there is a downside to the Jake that nobody has mentioned yet. A Jake works best at higher RPM.

One thing I have noticed with the retarder is that when it is on and I hit the brakes the retarder aids in stopping power to a noticeable degree. With the Jake, when we got down below about 20 it dropped out and while it wasn't like the coach accelerated, there was a noticeable loss of stopping assistance.

I guess if it could be done Perter's idea of having both would be the ideal.