RE: "Unloading a prop"
yes. 10x6 means 10 inch diameter with a 6 inch pitch. pitch means that if the propeller (screw) makes one full rotation (360 degrees) with no slippage ( like a screw through wood, as opposed to water or air) that it will have moved 6 inches. The higher the pitch,( all other things beiing equal) the faster the airplane ( 8 inches in one rotation compared to 6 inches in one rotation. There is no free lunch so it is harder to turn a higher pitch or larger diameter prop, so low pitch or higher diameter props climb/ accelerate better,( like low gear in a car) but are limited to a lower top speed than more pitch/ smaller diameter. There are many other factors that affect speed/ climb rates and that is why there is no "perfect prop". It is as much trial and error as science, but fortunately, most of the trials have already been done, leaving you with just a few reccommended props for you motor.
Have fun flying!!
Mike Kosatka