Here’s a scenario for JT’s Western Mainlines route, in which you’ll drive a GWR Class 150 on a stopping service down the Severn Beach Line. You’ll cover a distance of 13.6 miles and call at the following stations:

Severn Beach
St. Andrew’s Road
Avonmouth
Shirehampton
Sea Mills
Clifton Down
Redland
Montpelier
Stapleton Road
Lawrence Hill
Bristol Temple Meads

Duration ~ 44 minutes
Difficulty Level ~ Medium

(Considering how huge the Western Mainlines route is, I’m surprised that my computer was able to handle it without melting or the game crashing).

I’ve also recorded gameplay of this scenario for my YouTube channel:
https://www.youtube.com/watch?v=VhWOfNUaLx0

Lastly, here are the DLC requirements:

(Steam)
ECML ~ London to Peterborough
European Loco & Asset Pack
Network Southeast Class 159

(Alan Thomson Sim)
Class 800: GWR Pride by BHReskins

(Armstrong Powerhouse)
Class 150/2 Diesel Multiple Unit Pack
Class 158/159 (Cummins) Enhancement Pack
Class 800-803 Enhancement Pack

(Just Trains)
Voyager Advanced; not the 2019 version
Western Mainlines

(Superalbs)
Class 166 Great Western Railway