I am really impressed with my sons .270, flat shooting and i can shoot it all day long.
I shoot a 300 win mag, i can shoot it all day long also, but i feel it.
My boy shot a cow this year right at 200 yards with his 270 and she dropped. I shot a cow @ 275 with my 300 WM and she dropped. Both worked like they were supposed to.
I am a firm believer that it is more about where you put the bullet rather than what the cross sectional density of said bullet is.