My thoughts on your list:
1) Nightforce ATACR, 4-16 & 4-20: Great scopes, 4-20 has limited FOV at bottom
2) Leupold Mk5HD 3.6-18: Good scope, 44mm objective limits low light work. 35mm tube limits mount options. Expensive illumination option.
3) Kahles K318i: Kahles K318i is a great scope but pretty narrow FOV really limits its usability.
4) Razor G2 3-18 & 4.5-27 (thinking these are too heavy): I agree, too heavy for what you want
5) ZCO 420 (not sure I need to spend this for what I'm looking to accomplish).: ZCO 4-20 is the best ultra short out IMO. 36mm tube limits mount options.
Other scopes to consider:
There are a bunch and I'm sure you'll get a dozen recommendations, for 500 yards and in you can get away with 10x on top, no issue. New Steiner T6Xi 3-18x56 is worth checking out. Too early to tell how well it will perform as it was just released, but looks promising.
Out of curiosity, what don't you like about the NX8 4-32? Knowing that might help us narrow down some choices.