It isn't really temperature directly that causes mirage, it is the temperature difference between the ground and the air. I've had mirage issues with air temperatures in the 40°F range. The higher the ground temperature as opposed to the air temperature, the greater the mirage. The closer you are to the ground, the more you will be impacted by whatever mirage is present. The higher the magnification you use, of your optic, the more you will see the effects or the prevailing mirage.
20 power is more than enough magnification for 1000 yards! I too am near sighted but, with my scope properly adjusted, I have shot 7" groups at 1200 yards. 9" to 12" groups at that range are relatively common, when I get the wind read correct. Not too bad for my rifle setup and budget.
All true with regard to mirage, BUT, elevation above sea level dosent factor in, as you will find mirage at all elevations under certain conditions, even on cold below freezing days. As stated, less power is the only way to combat it.
That said, there are times when having the power available is an asset, especially in a hunting situation.
As for the 1st or 2nd focal plane argument, it would depend largely on the proposed use of the scope.
For a target shooter, there might be advantages to the 1st focal plane, and mil/mil, or moa/moa, and there could also be an advantage to 1/8 vs 1/4 clicks.
But no l/r hunter in his right mind will be ranging with a reticle anyway, and most would probably rather the reticle size remain constant regardless of power setting.
Frankly, many wont even care all that much about matching dial/reticle, especially the older guys who had no choices, but somehow grew up without it.
There is no doubt that the single most important factor in the success of long range shooting, and especially l/r hunting, has been the dialing of rifle scopes.
That said, it has been being done very successfully long before the modern day scopes even existed.
Which when we look back, wasent really very long ago when someone might say, (Whats a Nightforce)
Learning to use the dial so that a miss is a hit on the next shot is really all that matters, and it matters not the type of scope, or wether the miss was 4 feet or 4 inches if you understand how to correct for it, AND,
you or someone else saw where the first bullet landed.
Without that information nothing works, and with it take your pick because everything will.
