It's just my preference. The reticle on my 4.5-27x FFP looks like this:

[Linked Image from i.imgur.com]

It makes things pretty easy, where the reticles are one MOA at all magnifications. At 600 yds, I would just put the ninth reticle below center on the animal, not counting wind considerations. As discussed, I haven't shot past 380 yds recently, but it works at that distance, and I will check out the two ranges you mentioned when I get the time. Also, when I go out to my Colo. property, I can practice out to 800 yds or so. Last time I was there, however, they had a fire ban which means no shooting, unless at game.