I have found that when comparing props for racing, you really need to have someone with a stop watch out there timing your runs. Sometimes, your plane will sound and feel faster because it's turning more RPMs but in reality it is turning slower laps. About 40% of the race is turns and how well the plane pulls through those turns is a huge factor. You need straight away speed too, but if you are losing too much in the turns you fighting a losing battle. Props in this size are only a couple of buck a piece. You would be well advised to buy an assortment of sizes and get out to the course and fly them. Ground RPM is rarely a good indicator of what is going to happen once it is in the air and starts to unload. What works well on one airframe is not necessarily going to work on another. Your flying style has a lot to do with it too. If you fly tight turns, a given prop might work better for you than if you fly wider turns. There are a lot of factors but the stop watch won't lie. Lap times are what's important.

Blessings, Terry