I am not a sniper, nor have I ever competed in long range events.
I have a single scope that exceeds 10x. It's a Leupold Vari-X III 6.5-20x50mm, that resides on what used to be a dedicated varmint/target rig (.220 Swift).
Even out to 400 yards, or so, I never used the top end of the magnification in the field (prairie dogs). The field of view was too small, and the mirage too annoying. It usually ended up being set somewhere around 12-14x.
Now, that rifle has a different barrel and is a little more 'utilitarian', chambered for a wildcat equivalent to .243 Winchester. The only time it exceeds 10x, is when I'm shooting paper on a comfortable day. Even at 100 yards, barrel heat mirage is just too annoying on cold days or in the heat of the summer.
I have one 2-7x33mm (.444 Marlin with no iron sights) and one 3.5-10x40mm (.270 Winchester). Everything else is 3-9x40mm, even the scoped rimfires.
In the field, I rarely exceed 4x. Even on Antelope hunts where 400-500 yard shots might be considered as an option, the scopes usually stay down around 4x for a better field of view and mirage abatement.
In the last few years, I've given serious thought to going with fixed-power scopes on future builds/buys. 4x and 6x fixed scopes usually have great clarity, a fantastic field of view, lower weight, lower price tags, there's less to fail, and you only need to know the reticle's subtensions at a single magnification (if you care about that). Even if I were to build a "long range" target rig, I would likely slap exactly what this thread is about on the rifle - a fixed 10x.
I am not an expert, but in my experience...
Generally... At the same price point, a fixed power scope will be higher quality than a "low magnification" variable power scope (2-7x, 2.5-8x, 3-9x, etc). And, the "low magnification" variable power scope will be higher quality than a "high magnification" variable power scope (6.5-20x, 6-24x, 8-32x, etc).
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."