I've never really thought about it. It takes a LONG shot for either of those numbers to be relevant. 300Win is 950 FPE @ 800yds.
Flight time to 600 is ~.75 Sec. You add almost another 1/2 sec getting to 800. Too much time for the wind to act on the projectile and ENTIRELY too much time for the animal to move on it's own.
I'm working with a higher BC projectile that'll get the bullet to 800 in under 1-sec, dunno if that'll actually increase the distance I'm comfortable shooting or not. Right now 600 is pretty much my self-imposed limit with "hunting" rifles. I have on occasion packed along the 243AI or 7WSM "play" rifles. 16# and 19# respectively. 1# and 8oz triggers. Lots of rounds of ammo through both, 243AI is over 1200, 7WSM is on it's 2nd bbl. 12-42x56 Nightforce w/good flawless tracking and good reticles for precise wind holds. Both set up on a good BR-style front rest and something stable in the rear. In that case, assuming I have an excellent read on the wind, I'd shoot further than 600.
There are plenty of others who are more comfortable shooting further, no judgements, I just know what my limit is for big-game. Varmint's on the other hand, if I can see them, I'll happily fling away.