I've made some long (500-700yds) shots on stationary deer, but, they're really not very difficult. The wind hasn't really been a factor, nor has angle, temp, or elevation.
Those that stand out as "difficult" have all been 1-shot kill coyotes on the move past 300yds. Probably the most impressive was a loping coyote @ 380+ with my Kimber MT 7-08 and 6x42 Leupold. Mostly because it was pretty much a 90 degree left-to-right mover.
I got one @ 415ish with my 257Wby running pretty hard but he was going almost straight away and below me ~75-100 feet so I only had to cypher "vertical" lead and virtually no lateral lead.
Last was a coyote running away at a shallow quartering angle, 1st animal I pointed my then-newly re-barreled 1:8 22-250/75-gn A-max at. It was also the 1st time I'd used something with more horizontal reference than just a plain duplex, it's topped with a Leupold with TMR reticle. He was 350yds away and running hard, but, I was able to use the bottom tip of one of the horizontal hash marks as a reference for both estimated hold-over as well as lead.
