A lot of it is what you're used to having, plus the size of the target.
I shoot woodchucks out to no more than approximately 300 yards and I use 25X. They're pretty large, really. 15 inches by 6, give or take a couple. I don't think most long range guys go 25X at 1000 yards.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.