Yep will agree with you regarding the Garratts and fuel. In South Africa it was hard to tell front from back, as in later years they tended to run the GMAM class coal bunker first, to get the smoke out of the way of crew, etc. This may have added traction on upgrades with the heavier coal side first, until as you say it was low on coal!!
We saw a lot of violent slipped 4-8-4's in SA, and they tended to let them go. It was good to see engines worked hard, and not babied like you see here today on excursions and tourist railroads. I always enjoy seeing an engine accelerate quickly---like it has to be someplace in a hurry! Commuter trains around Port Elizabeth were like that, and a friend of mine sent me an awesome recording while riding a commuter train with a 15AR. It would thrash up to speed, cut off the throttle, and then coast into the next station and repeat this for the whole run. Having to keep scheduled times was a challenge to the crews, and great for the enthusiasts to enjoy! Real steam, real work!
Greg