I have hunted quite a bit with both the 300 Win Mag and the 338 win mag. I might catch hell for saying this but on Elk size game and moose as well, I have not seen a nickels worth of difference. I think this is because either gun is plenty for these animals and dead is dead. I don't have the manual handy but I would think with the bullet weights you mentioned, the 300 might have a bit of an edge in trajectory. For some reason I have never been impressed with the 338. I quess they are good for their intended purpose but I would skip passed it to the 375 H&H if I needed a rifle that big.