Extended parallel running in this scenario by sd70acesrule make for great fun!
One of the recent scenarios that I ran, BNSF Symbol CXYELUO by sd70acesrule had a really great section where you find yourself parallel running with another freight train. The combination of grade changes, speed limit changes and the other train being a bit more nimble mean that you’re having to do a lot of control to keep pace with the other train while not breaking the speed limit yourself. I always enjoy this kind of thing and the fact that this one lasts so long makes it all the more interesting! You can get this scenario from Steam Workshop here.