Either type of scope can be used for ranging as long as the operator is up to speed. The FFP simply allows you to use it on any magnification setting without having to do compensating math. You are probably right about having the scope dialed up for the exercise, and if the SFP unit is calibrated at max mag you're good to go. Some higher mag scopes in SFP have the calibrated setting at something lower than the max, and if you are shopping look for a model that provides a detent at the calibrated setting for consistent adjustment. Whichever type you choose, keep in mind that ranging with a reticle is somewhat challenging to do with great accuracy, as the ability to see the target clearly, variations in target size (both real and/or apparent) can all generate errors in range estimation sufficient to impair effectiveness in hitting said target. I consider reticle ranging to be a good skill for a rifleman to possess, but I fully acknowledge that at the distances where I need to be the most precise, my ability to use the skill is least likely to deliver the needed precision. My laser is my primary ranging tool for long distance, my topo map second, reticle ranging third.