The ACOG + RMR if you want the fastest transitions from close to far targets, get the RMR either piggy back or offset.
3.25 MOA dot gets bigger as you make it brighter, smaller as it gets dimmer. Big enough to be seen quickly but small enough to have the precision needed. I think the 1 MOA is a little small for a quick hitting back up system.
To me the best and fastest way to transition to the RMR is to rotate the rifle 45 degrees till your non dominant eye picks up the red dot. I like the ACOG / RMR combo but the chin weld thingy is bogus for me. If you are switching to RMR from ACOG, chances are it’s inside 25 yards and you shouldn’t have any issues making hits that way.
Offset to avoid height over bore issues. Piggy back RMR on top gives enough clearance for a nice solid side-of-chin-weld without the goggles banging off the optic. Keep in mind you can not used any magnified optic effectively with head mounted NODs. It's almost as bad as trying to take a pic of your rifle scope's reticle with your cell phone.
Even if it wasn't head mounted, NV compatibility is kind of a moot point with most ACOGs, and IIRC all of the LED powered ones, due to the eye relief of the optic.
In order to put an NV monocular behind an ACOG, with most mounts you would still have to bump the ACOG forward several rail slots in order to hard-mount your NVD, which would make it much more difficult to use for most people as a day optic.
Which essentially means you'd have to re-zero for use with and without NV (not to mention a drastically different stock position and cheek weld), which when coupled with how much light it will rob from the image intensifier makes it all around not worth it, "NV-capable" brightness settings or not.
Passive aiming is still not commonly or widely taught to conventional-side forces that are most commonly issued ACOGs, IR laser is the primary aiming method--but even when passive aiming is being taught and trained, it is usually considered more of a trade-off situation, you either go with an RDS and have passive aiming capabilities, or you go with a magnified optic and simply accept that you're not going to be able to do passive aiming, at least not easily. The compromise solution in many cases is a piggybacked or offset RDS--often when you see guys that are running a 1-x LPVO with an offset red dot, this is at least part of the reason which can cause confusion with folks who ask "why do they need an RDS when their optic has 1x?"
Everyone is different though so you wont know what works best until you try.
