I think a 600 yard hunting rifle should be expected to shoot 1/2MOA @ 100 yards, with verification out to your imposed limit of 600.
That means a 3" group at 600 from good conditions. No matter the weight or chambering of the rifle.
Because we all know those perfect conditions at the range and seldom, if ever, present on the mountain. I haven't ever, in 39 years of big game hunting, had a flat comfortable surface to shoot prone, with zero wind, and an animal perfectly broadside and relaxed, allowing for the perfect rock solid set up and zero adrenaline and slow heart rate, while hunting.
You start factoring in winds, weather, live game animals, adrenaline, humping up a mountain with a pounding heart, uncomfortable shooting positions, a makeshift rest, and your accuracy ability just doubled (or would that be halved) or more...minimum.
Too many people are thinking they have to build a 6.5-7lb all-in magnum for mountain hunting. Then can't shoot it well. 9lbs all-in is very doable and helps with a bit of forgiveness. I have very few rifles that are between 8.5 to 9lbs all-in. Nothing lighter than 8lbs with the exception of my .22LR.