I can't comment on that specific scope as I've never been talked into putting something that massive on a rifle, but I have several SII Big Sky's and SIIIs and they are all as good or better than their like priced / like featured competitors.
There are several Leupold Mk4 and VX3 on my most used scopes list and I could swap them out for Sightron versions without missing a beat.
I have NightForces on my 1,000 yard rifles but I do shoot with a couple fellows that have been using the Sightron scopes on their .308s. I have shot their rifles and compared the Sightron to my Nightforces and was surprised at the clarity of their optics. The glass seemed as good as Nightforce. The windage and elevation adjustments seemed smooth and positive. Tracking appeared to be stable as well. I can't tell you much about the durability since they have only been shooting them for the past 8 months or so.
Both guys are happy with their scopes and I even considered trying one for my AR10-T in .308.
I am a big Sightron fan. I do not have experience with the specific scope you are asking about. I have several Big Sky series scopes on some varmint hunting rifles and they are excellent. I believe they have better glass than the higher end Leupold and Burris scopes that I have at almost half the cost. Backed by lifetime warranty and from what all I have read have excellent customer service. Check Whittaker's or Ebay stores for best prices. The SII and Big Sky have a rebate on them right now, fyi.