You have it backwards. That isn't a stiffer spined arrow. Assuming that the .404 is correct (haven't checked) it is a weaker arrow than the .350 spined Vapor arrows.

That number is the amount of bend in the arrow. A .404 spined arrow bends .404 inches when tested and a .350 spined arrow only bends .350 inches when tested. The less it bends the stiffer the arrow.

In the maximas you should be looking at the 350's and not the 250's.