I am rigging a 4.7 Ezzy on a 430 skinny Ezzy so a bit of mast pokes through the top. I guess a 400 would be better but what difference does it make?
Will my setup be stiffer, more or less powerful, twitchier or don't worry about the difference?
it will be more powerful!!!
Because the IMCS rating for a 400 is 19? and the IMCS rating for a 430 is 21?
Which means, that the sail will rig with less "flick" being more powerful, aka wont be able to depower!
Hope it helps!
Definately get a 400 you WILL notice a difference!!!
As sails go Ezzies are pretty tolerant of improper mast stiffness. It should still breathe ok. It should just require more outhaul. They are not springy sails so you probably wont notice much difference in the feel. That's what I think.
Typically when you rig a sail on a mast that is too stiff it rigs very flat. This is because a large majority of wave sails use luff curve, to an extent, to create their depth. When a mast is too stiff it doesn't bend as much, hence the luff curve is less and they rig a lot flatter.
Ezzy's are a little different because they don't generate their shape purely from luff curve. This is why they rig quite differently to a lot of other sails. As NightsTalker said this makes them a little more tolerant to incorrect mast stiffness. It still won't be ideal and the mast won't flex off like a softer mast as easily but it still should be 'useable'. But as you say Cruiser it will be stiffer, twitchier and probably lose a bit of top end.
I have a 5m Ezzy (07 Wave SE) and rigged it on a 430, then I bought a 400 and rigged it on that.
To be honest I couldn't feel a heck of a lot of difference, apart from having 30cm less mast to throw around when gybing, and not having a bit of headstrap flapping around. The sail still feels SCHWEEEEET on either mast, maybe a bit lighter on the 400 
That said I now only rig it on the 400, because it's the 'better' thing to do. But I wouldn't call it $650 worth of better than the 430.
