For what it's worth, as you might have gathered, I am a big fan of 1.5-5 or 1.5-6 type optics for a variety of rifle styles, including "fighting rifles".
I have a Sightron S2 1.5-6x42 on a Robinson XCR, I have a Burris Signature Select 1.5-6x40 on a CZ 550 FS, and that Monarch Gold 1.5-6x42 looks good too - it looks nice and compact.
These can be VERY fast when set on the 1.5x setting and you can use them easily with both eyes open - almost as fast as a true 1x optic such as an ESD. Which is why guys going to Africa put them on DG rifles.
My theory on AR15 / AR10 type rifles vis a vis objective lens size is this: Given that you MUST put the line of sight of the optic up high anyway, why NOT get the extra advantages of the larger objective scopes (40, 44, & 50mm), such as larger field of view, less blackout, more light gathering, more magnification, etc.?? The only drawback is a little more weight & size, and that doesn't concern me overly for most of my rifles.
While I'm a fan of SMALL objective ("DMR") scopes for other rifle types with low sight lines (I have a Leupold 1-4x20mm on a shotgun, a Trijicon 1.25-4x24mm on a .22 rifle, and Bushnell 1-4x32 on a .22 rifle), it just makes very little sense to me to put one of these (what are being called "DMR" scopes) on an AR15 or similar and "waste" all that space down to the rail which could be utilized to accomodate a larger objective!
Remember, that "less soon blackout" advantage (for lack of a better way to describe it) on the larger objective scopes is a very real one, as it helps with rapid acquisition over a smaller objective - this is true with both ESDs and traditional optics.
1:7 is only needed for tracers-- all magazine length match bullets are fine in 1:8.
I would agree with that - but the Sabre Defense upper that you are contemplating with 1 in 7 has no DISadvantage either, relative to 1 in 8" for your purposes.
