What he said!I have shot F-Class nearly since its inception. We all started with 20X scopes as that is what we used in any sight HP matches. Then we found the 8-32X Nightforce BR scopes and didn't think we needed anything more, power wise. We all transitioned shortly after to 12-42X BR scopes and that is the minimum power I would recommend for any rifle, for mid-range or long range F-Class. Many are going to the 15-55 NF scopes as well as the Vortex Golden Eagle scopes now for that extra edge.
The target dot version of reticle is the best choice. The Mil-Dot, by design, is a huge dot. It was created to range items at distance, not precisely place a bullet on the exact portion of the letter X inside a 1/2 MOA target. A mil-dot will cover most of the X and 10 ring at 600 yards. Get a scope with a bigger objective as well, 50mm minimum, it makes a huge difference in the clarity of the scope in varying conditions. Used NF BR 12-42X scopes are for sale on this forum all the time for $1100 or so. Buy one with a NP-2DD reticle and you won't need anything more.
Scott