Have you tried some of the scenarios on the C&O Alleghany Sub?
Check out this great route at
http://www.coarw.com and look for the extra scenarios. You will need some donationware assets but these are well worth the small fee which goes to maintaining RWA amongst others.
All the available scenarios are modelled to prototype C&O/Chessie System/CSC operations of the late 60's till now.
There are several with 100 car trains consisting of 100 ton aluminium bathtub gondolas, so I think gross weight is something around 13000 tons including 3 or 4 3rd gen AC locos like ES44AC.
The same train needs 4 to 5 2nd gen DC locos like SD40-2 to get over the eastern continental divide at Alleghany, Va.
There are other scenarios with 140 car trains consisting of 75 ton hoppers, also with a gross weight of 13000-14000 tons which needs no less than 8 1st gen GP9's.
Imagine during the steam era those trains were handled by just one 530 ton 7500 hp Lima "superpower" H8 2-6-6-6 engine up front and a H8 pusher for the 10 mile 0.6% ruling grade between Ronceverte and Alleghany.
Both the hoppers and gondolas are "enhanced" with special scripts to allow simultaneous control of the pusher engines and the car's weights have been increased to fully loaded.
These trains feel and handle real heavy on both throttle and brakes, which you are required to handle with care and understanding. Running these trains clearly shows the deficiencies of the TS12 physics engine, as the couplers get pulled way from their sockets at the head end and pushed into their sockets at the rear end. When shoved really hard, the cars even snuggle up to each other and get skewed, but I have not yet derailed a train on purpose. Even in emergency it takes quite some distance to come to a stop as most of the run is uphill.
The route is not yet finished to be able to run the trains downhill into Clifton Forge, though the tracks are all laid just to about Covington. So you can practise controlling such a heavy train with dynamic brakes.
Currently there are still some issues with some of the RW2 scenarios under TS12 but these will be sorted in due course. Check the COARW forum, there are lots of posting by me and a few others concerning this great route and the quality scenarios. I did manage to get a few troublesome scenarios running on just one install of TS12 but unfortunately am not able to replicate why I was lucky.