Aaron, You are correct about the lighter duty lights costing a little less.
As far as size, the Corporal was made to fit on the dash as windshields began to slope more.
The RB11, MODEL 66, and DEPUTY, and CORPORAL all used the same 1195 50CP bulb and magnifiers, so all of those 4 had exactly the same brightness.
The SENIOR size lights had much larger magnifiers, offered a larger visual profile, and were shipped from the factory with a Whelen bulb # W44 which had a larger filament. This bulb was supposed to be brighter, but wasn't. These larger SENIOR size lights were a good deal brighter than the smaller lights.
That being said, these lights had a filament to magnifier height adjustment. If this adjustment was not made properly to give the best focal point ratio of filament to magnifier, the brightness suffered greatly. This was a problem with many making bulb changes, and made many think that the lights weren't very effective, when the dimmer brightness was due to maintenance error. When adjusted properly, these were nice and effective.
The # of lenses was always 3, and the FPM was always appx. 70-90
Not talking about the motors, these all had appx. the same life span. The HD motors would definitely make the light more HD, and add to the life span.