here is a quick reference pic of some bullets.
From left to right
6.5 -127, 270-140, 30-150 and 30-168
Notice the 6.5 is the lightest yet it is the longest and probably flies better than the stubby 30 cal 150 gr.
In reality all rifles mentioned in here can take an elk at 600, but Anyone that shoots that far needs to practice at those ranges a lot. Just because you have some big magnum doesn't mean you can hit a side of barn that far.
View attachment 681772
Never used a 150gr for elk, was always a min of 180gr and as much as 220gr.
Also never took a shot at more than 200yds, tho have seen lots of elk at 400 that others were shooting at and missing high, low, whatever.