I like using the Red Dot scope just because of the fact that it makes it a little harder. If I'm going to use a larger scope, I'm going to switch to a full-blown sniper rifle. I never have problems engaging targets out to 110 meters with the Red Dot Scope (the target is about the size of the actual dot on the scope, so cover your target with that dot, keep it covered, and fire about 3-5 shots).
There's some good combos in this post, though.
