For his tank and the way it's set up the WP series is a better choice. The tank is 7' long with center overflows. He needs a narrow flow with more velocity to get all the water moving around. Just my .02.
if you dont mind me asking, why do you want to downgrade the RW15? is it too much flow for the tank?
Im running a 60 in my standard 120 close to the half point on the w1 setting and love the wave action. I also have a 6105 and 6095 running full speed
Sorry but to much flow.