I have to agree with Zak Smith. I've been shooting 1000 yard matches for over 30 years and never saw the need for anything over 10X. (if you ever saw him shoot, you'd realize he knows what he's talking about).
With too much power your target gets washed out with mirage, and you loose your field of view.
300 to 600 you dont need much power at all, I do most of my shooting at those ranges with iron sights.
If your eyes are too old (like mine) to shoot irons, go to the drug store and buy a pair of reading glasses that allow to focus on your front sight.
You dont want to shoot without glasses anyway (whether scope or not).
I'm 61, my eyes suck. When I get glasses to focus on the front sight, I can't see to use the score (data) book, or chech the readings on my sights. So I get two pair of reading glasses, on my shooting eye I use the lense that focuses on the front sight, and for the none shootng eye, I put in the lense that allows me to focus on my score book and rear sight. You dont notices the differance when your shooting, even leaving both eyes open.
Nothing wrong with using scopes if thats the way you want to shoot, but dont let old eyes be an excuse for giving up iron sights.