In general higher voltage setups are more efficient because they use less current to get the same power. Volts x amps = watts. Current causes heat which is wasted power. So right now you have a 2930 Kv motor but you didn't say how many cells you are using with it. Lets assume you are running 3s. 3s x 2930 = 8790 /1800 = 4.88. That means that with the 1800 Kv motor you could go up to a 5s battery and keep the same gearing and you will have close to the same top end but better efficiency.