Me and my friend have both 496 mag and a 496 mag HO both with the Stage 2 upgrade and 120 degree stat. The 496 mag showed more increase. I have a Checkmate 240ZT wit the MAG and I gained 2-3 mph with a 26 4 blade bravo labbed prop. RPM were about 4700. The other boat is a 25 Baja Outlaw with the HO and it gained 1-2 mph. running a 25 stock Mirage Plus. Both engines seem to run cleaner. We both noticed way less soot on our transoms. I think it was worth it. Next winter I think I may go with a new cam kit Dustin is offering.