How much magnification for 1000 yds?

Use as much as the conditions and stages allow. During a normal match, I rarely run my scopes over 15-18x due to FOV and mirage. If you can get away with 25x, run it, but in most cases during comps you'll want mid to high teens.
 
Well, for the ones suggesting a low mag will work is also assuming that person’s eye sight is good or right glasses are used for correction ;). For a few of my buddies, they chat a hard tim seeing what I can at 10-14x. They required 18-25x.