You can frequently add a pickup to either the locomotive or the tender, and of course I common the pickups so that they're all active.
As far as the difference in scale MPH speed of upgrades, you need to consider a custom tach tape for that issue. Here's a direct link to a document by Hikel O Gauge describing custom tach tape generation. Attached to that post are also a set of PDF files with various count tach tapes that should work for most situations.
