The kid has a 6x Mil/Mil SWFA on her T3 .308, and while I have not spent much time shooting it, I found that ringing my steel that set out at 500 (1/2 size IPSC) was not challenging.
It is an amazingly simple, and rock solid little rifle.
It would make a dandy little coyote calling rifle too.
Personally I prefer 10X, but that is due to previous use of fixed 10s.