This is a tough one, basically the two most popular optics at this price point, the Burris XTR never made it past the initial fondling for me for a long range hunting optic good glass is only one part of the long range optic and for me lower on the list. Turrets and reticle are on the top of the list, deer and elk are easy to see and I don't really need ultra glass but I absolutely require good turrets with zero stop which the Vortex has but for ELR I have time to look at the turret and think but I'll be tying on 60 70 plus MOA and I need to see smaller targets and the SIII has been great for this. Shooting antelope last weekend out to 1200 yards both the Vortex and the SIII were stellar, never had any of these contrast or glare issues despite a clear MT day!!! Good luck choosing
High Fence, Low Fence, Stuck in the Fence, if I can Tag it and Eat it, it's Hunting!
And other reviews aren't any better. Sorry guys...newbie and first time "higher end" scope buyer wo/enough money to make a mistake. I'm really leaning towards use what I have for day time shooting and wait to get the best for when it counts (mostly early morning and late afternoon shooting)
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.
At 2,600 fps muzzle velocity (just a guess, seems reasonable for a 308, I've never loaded the 185's)...you'll only need appx. 33 MOA of adjustment...you said you had a 15 MOA rail...the Viper will do the job.