What Bob said. Application drives requirements.
I have both of the scopes you're considering, the Mark 8 on a 16" .308 AR and the 3-20x PMII on a 26" .260 GAP. Both are excellent in their specific applications. While I wish my M-TMR version had the dot type illumination the Horus has, I have no problem whatsoever using it without and that $500 I saved bought a lot of ball ammo for training. When on 1x you have a very well defined broken "T" reticle, illuminated even for when you're in the shadows, and maybe it's because I came up on iron sights for MOUT but I am running very fast with it. Of course I'm a Horus hater, so take that for what it's worth.