I must have had half a dozen of the SII 36X's over the years on my 30BR BR rigs w/o a single problem. To my eyes, the glass is right with the Weaver T36's and the Leupold 36 BR-D scopes. The later discontinued Big Sky versions have better optics. In fact, at last seasons NBRSA Score Nationals, I had a SII 36X Big Sky on. I'm less concerned with optics that tracking and keeping POI, though. As long as I can see the mirage clearly, I'm as happy as if I had a brain.
The SIII 36X45 and 45X45 ED 30MM scopes are a big step up in optics. On mine, it's like you can see 'through' the mirage to a clear target but still get the benefit of clearly seeing the mirage. Hard to explain....
Good shootin' -Al