I've used 6.5x20, 4x12, and 3x9, in that order and all Leupolds. I definately prefer the 3x9 for calling and I will probably go with a 1.5x5 on my current build for a lightweight calling AR.
I've never used anything bigger than a 40mm obj either, even though I call some under moonlight (snow). On Jan 11th I killed 2 in back to back stands at 200 and 160 yards, no problems seeing them with the 40mm at 02:00 am.
I'd like to try a lighted reticle, mostly for the cool factor, but to me its not worth the extra money or weight.