"Plan for the worst hope for the best" margin for error is kind of an individual thing, some are better at it than others. Uphill, downhill, rest for your rifle, etc, usually limit your range. If it looks like an iffy shot I'll pass for game animals I may take an iffy shot for a varmint. 350 is usually my limit, then IMO the ballistics get iffy, wind, temp human error, and a few other factors make reliable shots iffy. Study your ballistic tables see how much bullet drop you get at different ranges. I zero at two hundred and figure anything more than around a 14" drop is a no go.
I use nothing but Core Lokts mainly because many years ago I got a deal on some cases of it and have used it since. IMO it is a nice compromise between knocking them down and doing a lot of meat damage. It took me a while to figure out what bullet weight my rifle liked best, mine was 168 grain. But I use 180's on large game, Red Deer or Moose. One downside is the Core Lokt don't expand much through the lungs, shot placement is important.