I think the Colorado minimum specs make sense.The OP is in Colorado.
Along with bullet construction and placement is the self dicipline to let the big monster walk away if things aren't just right.
Lets not forget Colorado allows .40 roundballs for deer and .50 roundballs for elk muzzleloader season.
And,back in their day,the 25-20,the 32-20,the 25-35,the 32-40,and the like,along with the handgun/carbine rounds like the 38-40,the 44-40,etc took a lot of big game.Folks did not know enough ballistics to know their 44-40 was not a bison rifle so they just killed the bison.
Handgun hunters use .357's.,45ACP's,10mm's,44spls,45 colts to take deer.
I wouldn't mind having something like a mini-mauser in 6.5 BenchRest
I think the Grendel and SPC are workable,though I have no experience with them.
I think a 100 gr + 25 or 6.5 bullet at 2400 fps or so would be fine for 150 yd precise placement.
I'd feel just fine with a 10 inch twist .250 Savage