Nice pictures.
It's interesting to see that the smaller and older power seems to be confined to the northeast. Pan Am Railways also runs a lot of old Geeps and SDs as their mainline power, and uses old GP9s and SD9s for switching. In fact it's not unusual to see SD40s and GP40-2s still in operation here, unlike the Midwest where there is so much bigger, fancy, and modern locomotives pulling those 100km and faster freights across the plains.