I have both of them and from my experience you will not be able to tell which gun you shot the deer with. Both are very fine calibers with good down range ballistics. I reload my shells so there is not to much difference in costs. There is a difference in recoil, at least to me, I dont have any trouble shooting my 300, but there is a more recoil.
A 300 win mag is not needed for deer hunting, but I like shooting it. I glad that I have both.