All interesting comments. For pointwork, I only use large radius anyway so that won't be a problem, i'd sooner it look right than to be accurate, if that makes sense.
The layout i'm doing is totally fictitious location wise, but utilising rolling stock of the Derby area from 1990-2005, so I can get away with modellers licence as to the type of rail used for that part - I'm struggling to think of anywhere locally with bullhead, i'll have to look on flickr - I seem to recall Derby station area having bullhead in the very early 90s.