What are you running now?
Even without that information, I think that if you change to a 19 or 20 p 4 blade, you will plane faster, and be able to hold speed better ~20 mph. But it won't hold speed as well as perfect pass.
Without pp, or when I forget to turn in on, the speed control requires that I make check and adjust (really hard to make those tiny movements in the throttle!) every 30 seconds or so? When I used a 21p 3 blade, it was practically impossible to keep a consistent speed below 22.
When you talk to marinas and shops, they will usually tell you that you often have to experiment to find the prop that works best for you. Some shops "demo" props.
Check out http://www.kenyonpowerboats.com http://www.kenyonpowerboats.com/alpha1.htm
I think they had a very good exchange policy on propellers.
The best thing I found for getting the boat on plane faster is to keep weight in the front. I recently put some weight under the very front bow seat. I haven't tried that out yet.