About the same as between most any Kato and FVM...a lot! The first run of the Kato SD90MAC is about that slow also. If it wasn't for DCC, I'd be in a lot of trouble.
On DC, there's enough speed difference that IMHO it's not practical to MU regular speed and scale speed Atlas N scale locos.
There is a lot of difference between the old HIGH speed motor and the SLOW speed motor. There is also a big difference between the SLOW speed motor and the SCALE speed motor. I like the new Atlas SCALE speed motor so well that I have remotored almost all my old locos, both Atlas and Kato with the new Atlas SCALE speed motor.
Yes, I would have to guess, but that sounds about right. The SCALE speed motor is all about having your loco run closer to scale speed without the aid of a DCC decoder.
No, with DCC it does not matter. You can define an individual speed curve for every loco and match them together. It takes a little time, but is well worth the effort. Have Fun Michael
Yes, it does matter, you can only do so much with DCC, it does help but a high and slow speed motor still runs like crap at slow speeds. The Atlas Scale speed motor runs great without any help from the DCC decoder, so with a decoder they only run better.