You want a bullet that'll exit both shoulders on an elk or bear...I suggest ya pick a 338/408 or some varient of that combo in 300 grainers or better yet a 50 cal. Asking that of a 7mm or 30 cal in the heaviest of bullet weights is asking for trouble. If you do however manage to make a shoulder shot at 800 the animal will most likely be disabled enough to allow a follow up shot but imo thats still a poor decision to make at 800 yards if a better shot does not present itself.
Any bullet at 800 yards shouldnt be placed in the shoulders if thats the only shot you have to take then you should wait for a more opportune shot even if it means waiting.
At 800 yards if placed in the right area the SMK's and Berger's will do what is needed of them.
This all centers around shot placement and if you have the opportunity to make a good shot.
If you have a gun that is capable of shooting half moa at 800 then you have enough precision to make a heart/lung crtical shot.
I recently did some load development with my 300 wsm
and shot at 800 yards it was close to moa. With the 190 grain bergers in southern white tail country the shock value if placed close to the vitals will probably net a kill be it some tracking will be involved it would still work.
However I wont take that shot until I can get it under 8 inches I'd presonally like to see 4 to 5 inches even 6 inches for a more comfortable shot.
This is just my opinions and I aint calling anyone out on it just an observation and personal preference.