
The R7 425 is designed for "players" (read Lower Handicappers) with consistent swings and who like, and can, shape the ball.
The R7 425 is more forgiving and is designed for "golfers" (like me) who have less consistent swings (like me) who "think" they can shape the ball (like me) but really need a club which is more forgiving (like me).
As fengibbon says, the key is DEFINITELY to get yourself fitted. I have tried the Burner, SuperQuad, R4 425 and couldn't find a stock shaft that suited me...
I have an R7 400, too - it is relegated to the trial club for banging out different paint jobs and chasing the local chavs down the road on their petrol-to-noise-converters (50cc scooters).