I dont have a win mag, but do have a 300 wby. Before I bought the gun, I looked over all the ballistics and noticed that the only difference in a 06 and 300 is that the 300 will push a bigger bullet further and faster. As a question of weather you need one, depends on the reason. If you think you need one because a 30-06 is too small. That would not be true. A good old 06 will take anything you want to shoot. Now if you think you need on because it would be cool to have another gun, Id say, go for it. I didnt need a 300 wby, I have a 06, 270, 308, but just wanted one.