I'll go first with my own very limited knowledge and thoughts
A. I know the four coloured Valtra are rare and valuable. These were available to dealers or something like that, I think I've read.
B. I really like the Farm Toy Forums Britains specials. I have two gunmetal Ford 5000's, two of the Ford 7000's with the harrow and also the gunmetal Case. I know there are more of these but its not easy to get holistic information on them. I need to get my hands on the industrial Ford 5000. I never used to like the look if it, but now I kinda want it!