According to my copy of Rolls Royce's book about the jet engine, the limiting speed of the engine is its exhaust velocity because the velocity term in the momentum equation is the difference between exhaust gas velocity and free stream velocity. Therefore in effect a jet engine does have a zero thrust speed and thrust reduces with forward speed, somewhat like it does with a prop or d/f though it is not as simple because the intake effects considerably alter the rate of loss compared to the fairly simple straight line loss of a prop/fan . A major difference is that the jet's exhaust velocity is vastly higher than that of a prop or fan, and thus its zero thrust speed is commensurately much higher. At full throttle it is not unusual for the exhaust to be at the local speed of sound, which being at a very high temperature is much higher than the speed of sound of the surrounding air. Since the zero thrust speed and rate of loss of thrust is related to the exhaust velocity, it follows that two engines with identical static thrust but with different exhaust velocities will have different dynamic thrusts and therefore different top speeds. How much this translates to different speeds for the aircraft is limited though, bearing in mind that at the speeds at which model aircraft operate the increase in speed will be heavily affected by the square rule in the drag equation so it will take a big increase in available thrust to generate any noticeable change in speed.
The actual rpm of the jet engine is not particularly relevant, it is dictated by the need to generate optimum turbine blade speed and in a small diameter it requires a higher rpm to get the same blade speed in what may be an exhaust velocity of the same speed between a large and small engine.