I would split them BUT if they are part of a set split them in such a way that if one box goes missing the part that arrives may still be of some use. If one box goes missing any insurance will only pay out on whats missing even if it makes the part that arrives useless.

Interparcel are good, there prices are not the lowest but they are based in the UK and answer the telephone, most others do not! 

You could also try parcelflight once yu have your true rates and dimensions give them a call and see what they can offer on "Spot Rates" again they are UK based and answer the telephone.

There are others that are cheaper but you get what you pay for.