Noted performance recorder O S Nock described the GWRs 43xx mogul as
"A total synthesis of standard parts, using the outside cylinders of the Saint, the wheels of 31xx 2-6-2 tank and the No.4 boiler, in its superheated form." (British Locomotives of the 20th Century)
The 31xx engines were the precursors of the final 5101 class 'large prairie' design, however while the 2-6-2 was ideal for branch and suburban duties Churchward had originally intended his secondary mainline service mixed traffic tender engine to be a 4-6-0. His thoughts were revised after visiting the USA to review American design practice and observing 2-6-0 locomotives in widespread use.
There is no doubt that the 43xx was a huge step forward in British locomotive engineering and the engines were possibly so successful in their 'behind the scenes' role that the class is almost overlooked. Named express passenger engines taking the limelight while the 2-6-0s competently kept the GWRs good revenues rolling in. O S Nock also says of the 43xx moguls, they
"could handle the heavy goods work as well as the 'Aberdares' and could run up to 70 mph with passenger trains, in other words they were the ideal mixed traffic locomotive"
Could they be improved? The 68xx Grange was a 4-6-0 rebuild using 43xx wheels and motion, but with a higher boiler pressure crews thought them better than a Hall... But in 1911 climbing into the cab of a new 43 was a step of decades into the future!