Hi!
SuperAirborne...It isn't that easy to tell you what makes your/our planes go fast , you can help us by telling what airplane /engine you have in mind.
For instance in my F3D pylonracer powered by a 6.5cc twostroke engine,weighting 2.2kg a carbon prop ( hand made) that has a pitch of 7.5" and a diameter of 7.1/4" the engine turns this prop at around 30000rpm on the ground. Straight line speed is around 350-375km/h. Straight up speed the same or thereabout , climbing straight up for as long as ...well it disappears so fast that I have not dared to try it for any longer moments.

In my SIG CAP 231 EX (ARF aerobatic airplane ) weighting 5kg I use a MVVS 25cc two stroke that swings a 18x6" Menz prop. Top speed is around 150-175km/h and climbing performance is good but not as good as my F3D racer. The difference is the CAP can stand still in the air with its nose pointing sraight up and will accelerate straight up as far as I can see it when I give full power. Its slow accelerating capabilities are thus much better than the smaller racers.

My small electric aerobatic airplane (Icarus) at 150-160g, powered by a the smallest AXI outrunner motor is swinging a GWS 8x4.3 prop at around 6500-7000rpm and top speed is around 30km/h.
Climbing straight up is out of sight as the other airplanes but climbing speed is much slower. This airplane hovers at 1/2 throttle.

So saying that a certain pitch or certain diameter produces speed is not true..it's as always a combination of things.
So tell us more what airplane/engine you have and we could perhaps help you.

Regards!
Jan K
Sweden