I shoot on 42x every time I can at 300 yards (F-Class Mid Range Match). How about 14x for every 100 yards!
There is a very important saying, "Aim Small, Miss Small".
Per above, there are a number of factors that can limit your useful magnification range:
- Atmospheric, Mirage will be the main one, but Humidity can also limit the useful range
- Field of View, there are times that you will need a wider FOV, could be Situational Awareness or the need to spot misses
Your situation and application will also dictate what makes sense in terms of a useful magnification range. Per Rob's comment, you will need a lot less magnification for a Minute of Man target versus a MOA target. You also have to consider if Target DRI (Detection, Recognition, Identification) is in play. With a paper or steel target on a square range there is no need for Target DRI, but if you get into real world shooting or competitive shooting with unknown targets, and you first have to be able to find and positively identify your target, and more magnification always helps in that process.
In terms of the 1x per 100 yard crowd, they are usually Parrots repeating what was said based on the methodology from 30-40 years ago. If you look at the standard optics from 30-40 years ago where 10x was the top end, to the optics of today where 50x-60x is the top end, it is not hard to figure out where things have gone.
Scopes with 3x-6x on the Low End, and 20x-25x on the Top End, are very hard to beat for most shooting applications. There are times when more is better, but it tends to be limited to some very specific situations and applications.
Bottom Line, you can always dial back down if you need to, however you can't dial up to a power that you don't have!