its 450 at 4 ohms. and yes. more power is more volume. but dont expect a monumental difference, you have to have 5 times more power to double your volume. with that youd be looking at a 3db or so gain in volume. you want more speaker area. get more spekaers if you need more volume.
an 810 and the 3pro. i can somewhat see volume being an issue. but it shouldnt be to much of a problem. well if he really needs more volume tell him to sell the 3pro and get a svt classic. hell be heard without a problem.