A <i>very</i> good rotor. To be honest, the only thing affected by the radius of the sprinkler is the precipitation rate, GPM affects the nozzle size you have to use. It's wise to not go above the GPM capacity of the mainline, so If you have a 12 GPM mainline, with a 2.0 gallon nozzle in the sprinkler head, this means you can use 6 sprinklers on that particular valve. I prefer to use 1/2 elbows on the ends of the line, even if a 3/4" sprinkler has to be threaded into it. This keeps the pressure up for the way end sprinklers if you have a long line, and it distributes the water evenly in the line. To get from the 1/2" elbow to the 3/4" inlet of the sprinkler, you need a 3/4x1/2 nipple. You can find them in the online store in the "Misc" section.
Thank you!