Here in Australia there is rough and tough country that is good but there is a lot of downright poor country that even Brahmans don't do well on. I have seen SD breeders send cattle into Northern Australia and they performed poorly,maybe not due to entirely to the country but to other climatic anomalies,ticks flies and the heat etc. I am in the process of selling my late father's property about 75 miles south east of us (alt 400 feet av rain 40 ") It is country that British breeds fail to do well in though Droughtmasters and other Brahman crosses do well. We live at 3,000 feet in basalt and granite country with plenty of minerals etc available naturally to our cattle,so they do well here.
One thing I have noticed with South Devons is that after they get a bit lean over winter,they respond much more quickly to the change in seasonal conditions than our Brahmans do. Herefords have the same response for us as well.
Thank you for the comments
Colin