Lots of studies have been done onthis, and 7-8 power is optimal for the human eye. If you get larger objective lenses like 40 or over, you can resolve movment at 1000 yards. Saying all that I have a 8X and 10X and like them both.

Go out with cheap glass, after glassing hundreds of yards for 3 hours and you can wind up with a bad headache. I like the higher end Leica's and stieners too. The older gold ring leup's are great too. I really want a set of EL's. But my budget can't go over 800 as rough as I am on things.