I have a sidewinder 30 6-24x56 true mill at 20x. It's a good scope. It has the big side wheel, illuminated retical, and a few other nice features.
The 20x true mill feature has one real advantage, because it's a second focal plane scope the space between the subtentions (or mill dots) grows when the magnification is reduced. That will allow you to turn the power on the scope down and increase the range you can engage targets. My fx verminator mk2 is running 770 fps with 18 gr jsb's, if I turn my scope to 6x I can engage targets out to 170 yards without a tilted shimmer or adjustable scope base. Hope this helps