I have a Mark4 10X I like a lot, no problems seeing smaller targets so far but I've only shot it out to 568 yards. I can't see why a 10 or 12 power wouldn't be fine for hunting out to at least 600 yards.
We are in the age of "Power" and in some cases more power can be a detriment.
The reason we tend to gravitate to variable scopes is so we can use the power that best suites
the situation.
As stated earlier, mirage can be a problem on the higher power unless you can read it well
and it doesen't distract you. with a variable scope you can crank it up to read the mirage
and then go down to a level that it doesent appear. The same thing with heart beat.
If you consider that 1000 to 2000 yard matches are held that require iron sites (NO SCOPES)
it is obvious that you can shoot long distances without big magnification.
If you are shooting long range targets under ideal conditions (Good rest/positions) more power
can be used . But if these conditions are not perfict(Like when hunting) less is sometimes more.
The very first match I shot as a young man was a 600 yard 20 shot target match. conditions
were not perfict and we had to hold the rifle with a sling(No Rest). everyone had high power
scopes up to 32 power, I had an old K 8 Weaver on my deer rifle and just wanted to see how
well I could do against target rifles with high power scopes.
I knew nothing about mirage and reading the wind, so all I did was to try not to shame myself
and shoot best I could. I can remember hearing those guys talk about all those things that
were affecting the bullet impact and they were continually changing there zero.
When the match finished and scores were counted, somehow I had won. The point is, that more
magnification can help if you can use it but sometimes it can hurt.
So, A 10 to 12 power scope will work very good if it has parallax adjustments and you are shooting
targets of known distances. More power may help you group but may not help the score.
There is a usable limit on power of a fixed power depending on conditions. For hunting the
variables have an edge because you can lower them down to the lowest power for running shots
and if a long shot presents it's self crank it up to the level needed.
I still have and use many fixed power scopes that are perfict for there intended use.
Sorry to ramble on ,just trying to clear up the question.
J E CUSTOM