More revs not always make the airframe move faster.
The limit to higher speeds is the drag force, which grows exponentially with the speed.
The only thing that can increase speed is an opposite force: thrust force.
(The most common thing that can stop high speeds in a dime is called flutter, watch for it!!).[sm=75_75.gif]

When your model flies level at max speed, the prop-engine is developing the max forward force that it can.
When you dive from that condition, the component of the weight force adds to the thrust force, increasing the forward speed of the model for your low pass.
At that point, the AOA of the blades of the prop decreases, they lift less (less thrust), and tend to move faster driven by the engine (rpm's increase much).
Then, the air pump that the crankcase of the engine is, sucks faster, the carburetor throat becomes a bottle neck (sorry, no more air can go thru), vacuum sucks more fuel from the spray bar, which makes the mix too rich for timely combustion (rich mix burns slower and cooler).

The result is what is called "four-cycling", the engine actually is firing every other revolution.
On one stroke, the combustion is interrupted by too rich a mixture.
That rich mixture gets ejected on the following downstroke, after which a fresh charge enters the combustion chamber that the plug may be able to fire, if it is not too "oily" and cool.

If you have available power, like the case of your fast Revolver, achieving the highest thust force is the way to go for max speed.
Unfortunately, the relation between rpm's and thrust force is not lineal, as any engine performance chart shows.

The right combination of engine, prop diameter and pitch will provide the max thrust force, which is seldom found at hyper-rpm's.
It has been said that the max thrust is found at a range of rpm's at which any engine can develop max torque.
That range of rpm's is always below the max rpm that the manufacturer recommends as "safe" for the engine.
In practical terms: select the max prop diameter that your airframe (ground clearance) can take, and increase prop pitch until the engine is loaded to rev's in the range of max torque.
From that point, follow a fine tune, playing with diameter and pitch in small increments, until finding the sweet spot that pleases you.

Just experiment, this staff is fun!