You have some good info, and bring up some good questions zoyd.
I use a competition die for my Swede target rifle, the main reason is because I received the die with the rifle. Swede's have a long throat and it makes a difference how far out the bullet is seated and the length is different in each of my rifles.
I've always thought this has to do with bullet jump to the rifling but I am not sure why it makes a difference. Hopefully someone with more knowledge than I can help.