I would say if you can shoot 1000yds, an 18" will do it. A 20" may be a bit better, but not so much if you can do your part. A lot goes into shooting that far, and if you can do it, the 18" will do it for you. I'm will not tell you stay shorter. It would be easier to lug around, but you need to be happy with it. My biggest thing for you is 1-10. After that, you need to figure out what you will want. I hope it helps.