Hmmm... I would have used 430 bottom and 400 top. The reasoning is that the 400 bottom with rigid mast extension would make the bottom stiffer in it's curve, much like a 430 bottom.
Using a stiffer 430 top would make the curve very different from what the sail was designed for.
I don't think the Ezzy recommendations are a good guide as they probably have designed that particulat sail around that specific curve.
But, as always, the answer is as stated above: Suck it and see.........