A friend of mine was a part owner of a 50, and I used to be a member of a group who bought some 55s, as another 55 owning group said 47s make good test loads and you have to be carefull when towing them over 100mph as you can break them

A truely expensive beast to run!
Given a 47 was designed as a multi use loco, the 90mph speed limit (although I know of drivers who have taken them past the 100 mark) is of little issue on the vast majority of the UK railways, even less so in preservation.
A 55 was designed as a passenger loco and hence cant pull the same load all day long (without buggering an engine

!)
Its the nice big Sulzer lump I like, plus the DandM brake setup is pretty interesting!
I still like the 20's though!
Biggest problem with the EE stuff is the rust.....they are the Leylands of the railway world. We have the EE preservation group on site who have an 08, 2 off 20's, a 37 and a 73. (note 20154 is a hell of an engine with a suspected 1200 bhp at the rails!)
Interestingly, we had a visiting 31 (from BAR) at the Gala, the driver (who I know well), drives these regularly on the main line and says that you have to knock the ETS off as you leave with a passenger train to get enough grunt to get them upto speed!