V20 with a 140 johnson

[thebottomfish]

Looking for some top speed numbers, I have a v20 with a johnson 140 on it, and with my stainless prop am hitting 34mph at my best, the motor is only turning 5200 rpm, but I'm not sure I want to go from a 13 3/8x 17 to a 13 pitch to get in the right rpm, I think that would hurt my top speed...am I right? Convince me otherwise!
I'm not only after top speed here, my cruise @ 4000 is 23mph and I'd really like to bump that up

Thanks!