The standard 3.89 is the light duty axle used on the small chassis cars. e.g. GT6, Vitesse 2 Litre, Spitfire Mk4, Dolomite 1500. Ok for normal road use in those cars, but not competition. The standard 3.9 is a heaver duty axle and was used on the 5 speed TR7.
The standard 4.875 axle was used in Herald 948 Saloon and Standard Eight. Again light duty.
Other rations were-
The standard 4.55 axle was used in the Herald 948 Convertible/Coupe and Standard 10. Again light duty.
The standard 4.11 (Different from 4.1 axle) axle was used in Herald 1200, Herald 13/60, Spitfire up to M