Short answer (guess)
430 top with 400 bottom. Reason: Powerex is average to flex top in curvature(12-14). Late Severnes are stiff top (around 10). Try it first and see.
Long answer: I had 07/08 Blades. Looked best with Powerex compared to Maui Sails RDM (and so got rid of it). Now have 09 S1s. Look best with Gaastra 100 RDM (unable to find a Redline in US) compared to Powerex.