If we can be reasonably certain that Larwood bowled around the 140 kph mark and was seriously quick, then why not look for eye-witness comparisons between pre-WW1 Test bowlers and Larwood?
Opinions differed, as you might expect.
Pelham Warner – Larwood as fast as any in history and the most accurate. Pre-WW1, Kortright (similar to Larwood in pace) then Ernest Jones, Kotze and Cotter. Cyril Docker (AIF) in same bracket. Also later Constantine when at peak. Lockwood superior bowler to Richardson.
Bill Lockwood – Larwood as fast as any pre-WW1 except Richardson, who was also the best.
Herbert Strudwick (1959) – Richardson the fastest and best.
Neville Cardus – Richardson the greatest.
CB Fry – Jones fastest spells. Kortright fastest single deliveries.
FS Jackson – Jones the best pre-WW1.
Bob Crockett – Jones faster than anyone including Larwood. Arthur Fielder the best.
Hendren – Gregory fastest bowler faced 1907-38.
Sutcliffe – Gregory faster than McDonald.
Oldfield thought the opposite.
Hobbs – Gregory not as fast as he looked.
Christopher Nicole - Tyrell Johnson (1930s) quickest West Indian before Wes Hall.
Kortright hardly ever bowled short. Richardson only rarely.