With a couple of Class 101s for company! I've been playing around with GWE in the scenario planner to get around the red light bug affecting services from most platforms, and discovered you can create some busy-ish scenarios on GWE even with the bug not yet fixed. A train can depart from Reading platform 11 with a clear route through to London on the fast line. And a train can depart from London Paddington Platform 13 with a clear route to Reading along the slow line. If you place some trains on the intermediate slow line platforms they'll run too, I tried the same with the fast line but the trains didn't move, but so long as you keep the path ahead of your train clear you can still put the BR-era diesels through their paces! This has confirmed GWE as my fav route, though it may be a bit boring and flat, it's really good for just letting the BR era locos run up to speed without having to worry about speed limits.