What rpm are you turning at 67 mph? Also,is it gps or regular speedo?Going to be hard to have the best of both world(cruise and top end) with a stock 454. My 280 came with an HP500efi Merc Racing(500 hp) and it had a B1 24 pitch.Top end was 72 mph gps at 5400.So the 24 you have is going to be very close.Maybe lab it.You'll lose a little cruise but it will spln higher on the top and probably be faster. Still need to know what it turns on the top at 67 though. That's where you gotta start.

If you answer Griff's question, it'll be alot easier to help you.

Also, do you have a diffuser ring on the prop ect? X-dim?

Verbi's 24 max could be the way to go tho.