Re: using a 10x zoom out to 1000m ?
For my needs, I try to define my entire mission before deciding to spend hard earned money on a good scope. This means consideration for the full range of my shooting.
One factor that must be considered is the thickness of the reticle at max power when shooting small targets at 1000. Larger targets are obviously easier to see. I have shot 10" X 17" steel targets at 1050, using a USO 3.2-17X. It is no problem to see the target, but, the Horus H-25 reticle I ordered is relatively thick and obscured most of the target. With a finer reticle, you can "quarter" the target clearly and break the shot cleaner. I had the good fortune to shoot Vern Harrison's original "flea" scope on 18X with a very fine floating center dot on the same target, and the difference was very notable.
10X at 1000 lessens the reticle thickness with FFP (another consideration) but makes the small target harder to see. I just got a USO 1.8-19X for my new LMT 308, and I have the same concern as you. I got the JNG Mil reticle, which John III at USO told me was finer than one of the other mil reticles I asked about. My mission right now makes it an 800 yard rifle, but I am certainly going to test it out to 1000. You also need to consider how close you will be shooting. My 16" 308, although not a "battle rifle" in my mind, does lend itself to faster close in shots than a 24" bolt gun and a low bottom magnification was necessary for my mission.
Again, your mission will define the magnification required; larger targets allow a lower magnification. The reticle thickness is still a key factor and one that I don't hear a lot of discussion on.
When they can make a 1-15X that is usable in close with both eyes open, the perfect scope for my mission with a 16" 308 will be at hand. I won't hold my breath.