I ask what scopes people use at our local long range matches. Be it 600 yards or 1000 yards the most common scope magnification is 20X to 24X. I shot with a 6X scope at 1000 yards and the marking spotter was indistinct and it was difficult to quarter the ten ring. I am using a 20X and I can see plenty. I have not taken any of my 16X scopes out, but I think you could see very well with any magnification from 16 to 20X.
High magnification can be a disadvantage as the image gets darker and the ills effects of mirage actually make things less distinct. Many times I have seen the bullet hole only when I dial down the magnification. Also, guys who use 32X + scope have a tendency to cross fire because the field of view is so limited and they forget to check each shot to see that they are on their target.
Weaver T series (T-20, T-24, etc) scopes are very popular based on cost. The shooters using them tell me they are clear and have repeatable clicks.
If I'm not shooting, I'm reloading.