Whatever is best value. I havn't dismissed the Syil X4 Speedmaster at £4150, but would have to be convinced of it giving good value - and being resellable without too much loss if not. On the other hand, if I bought a Bedford 190 at £850 and it was a poor basis because of design problems then I would regard that as a waste of money. I guess I am asking for things like "avoid XXXXXX as it can't machine cold butter" or "There is no practical way to fit good steppers/servos to YYYYY"