Consider shooting without NR, if your images need help do that in post but most will say they look great w/o NR. I tell the people who shoot for me to turn it off because it makes skin muddy and plasticy, more soon the Nikon cameras to be honest, but I have seen the 5dm3 NR and it looks pretty good, still its better to leave that detail control in your hands.
Your file size increases as you go higher in iso. I have no idea why this is but it just is and i am ok with that. Your lower file size is nothing to be concerned about.