I haven't sailed the hellcat myself, but the Kodes are not so sensitive when it comes to sail types as long as you stay away from the full on race stuff.
5.4-6.2 seems like a perfect step.
Flex and materials: At this size the Wood Carbon will probably feel the nicest. The Kode is a comparatively calm shape as it is and I don't think you will fins the WoodCarbon to stiff. But on the other hand, weight difference is not as big on the big Kodes, so you have to relate the weight saving to the extra cost.