I have a very accurate AR in .223 Wylde which is currently topped with an old (very old, perhaps mid '70s?) Leupold fixed 12X40mm (one-inch tube) with adjustable objective (OA). It has been upgraded with a mil dot reticle and targets knobs (MOA adjustments). I've been using it happily. But then along comes a friend who offers me an opportunity to trade my old Leupold for his basically brand new Vortex Viper VPR-M-06MD 6.5-20x50 PA with mil dot reticle and MOA adjustments. I'm hoping for some suggestions, advice, recommendations from the seasoned and knowledgeable contributors here as to which would be the better scope for my application. I'm shooting prone off of a bipod and punching paper (and clays and golf balls and other assorted targets) at long distances (>700+ yards with 80-grainers loaded one at a time). I went to a fixed power because my previous scope (Zeiss Conquest) shifted impact with shift in magnification. My first priority, then, in choosing between these two is I cannot tolerate a variable that shifts impact when changing magnification! I would love to upgrade to the Vortex's higher magnification (my main reason for considering this trade), 30mm tube (although it really doesn't provide much more elevation: 68 moa actual vs. 55 actual), and the similar customer support. So with this scenario in mind, which scope would you think would be the better choice? Which one of these two would you choose for this application?