I have just looked in Smith's 'Gas Air and Spring Guns of the World', and on Page 123 he sets out some technical data for both the BSA Cadet and Cadet Major.
The velocity of the Cadet and Cadet Major are given as - 405 & 450 feet per second APPROXIMATELY.
It is my experience that Smith is rather conservative on his velocity figures, so with that in mind I would say that in good condition the guns should put out 450 f.p.s for the Cadet, and 500 f.p.s for the Cadet Major.
BSA, in their advertising literature gave the effective ranges of the two guns as 30 yds for the Cadet, and 40 yds for the Cadet Major (effective range againt vermin)