Re: Viper vs. SIII ???
I went through this exact decision a few months ago, and I ended up going with the Viper PST 6-24x50 FFP MOA. Glad I did. I love the FFP for wind hold-off at any magnification, ranging, etc, and the ZS and IR are nice features. The IR on the PST is great. Even on max brightness, it's very serviceable at twilight.
The 65MOA that is listed in the specs turned out to be 69MOA in my particular scope. With a 20MOA base and Burris Sig rings with the "10" inserts in front and rear, I have plenty of elevation to reach well beyond 1000 yards with my .243AI. The adjustments measured dead-on accurate and repeatable on my optical grid.
The optics are crystal clear until you get to over 20x, and then they are still very good, but not Zeiss/Swaro good. To give you an idea, on 6x my PST is brighter, and has better resolution than my FX3 6x42, which is an amazing optical device for the price.
I would suggest that the SIII may be better for formal competition, but to me the PST seems like a better do-it-all, hunting/tactical/competition scope.