I switched from a 905S 8.5 Grafalloy Blue S to a 910D3 9.5 (D1 position) with a Fuji Rombax 6Z08 X-Flex.  Obviously, there are more variables than just the head, but both are comparably stout shafts, despite the difference in flex designation.  I am hitting the 910D3 both farther and straighter than I ever hit the 905S.  IMO the 910D3 is the natural progression from the 905S.

Fairways and greens!

Neil