I frequently had to use them between Victoria and East Croydon when I was acting for clients in the Croydon area.
The other thing about the Southern 377s is that they played a major role in some of the Microsoft Train Simulator add-ons: London South-East, and South Coast. I had the original MSTS and "drove" the 377 to various virtual destinations including Brighton, Ford (change here for the open prison), Littlehampton, Bognor Regis, Worthing, etc.
Hmm, I think 100mph is equivalent to 161km/h.
128km/h is more like 80mph