I would opt for the higher power, given your range requirements and the cartridge. Out past 100, those extra X's sure are nice, especially on deer sized game.
As far as rings go, opt for 3 - I didn't use rosin or labels inside the rings on mine, and 2 big, wide strong rings wouldn't hold it on my revolver. I had to remount the scope after some frustration. Play it safe and use 3...