that is the same nitrous kit im putting on my boat from people who have tried yhe 150 hp have picked up between 450-600 rpm.As for the impeller a b cut would probably pick up speed but will increase your rpm by about 350-500 rpm.It helps get your motor to the peak hp range.If your motors hp peaks at 52-5300 then a b would do you no good.I would call a pump guy to have him explain it better.I have talked to jack at mpd(949)631-2040 about his and had him cut mine down too.Went from an a to an A-B and picked up450rpm but then again my motor peaks at 55-5600 so my new one is cut to a b+.Remember once you cut down its permanent meaning you can only cut smaller and cant go back to an a cut unless you buy a new impeller.I was talked into trying an A-b cut first to see if it helps before going to far and im glad i did as i think the b+ cut will work great.