I've just got hold of a NP Zone 4.5 and now need a 400 mast for it. Any advice?

I've seen the Amex Katana 65% RDM which looks good value at £170, but NP sails generally need a flex top mast. Has anyone got experience of the Amex mast on NP sails? The 2 Amex masts in the baords test were more standard flex, rather than flex or stiff top.

Or should I save up a touch more and go for the best NP mast I can afford or a Tushingham RD mast, which according to the Boards test lately is more flex top, or any other?

Ta
bob