I think you will be happy with the 243. I used it for many years for deer and it pretty much stopped them on the spot. I had one that went 10 feet but the rest dropped where they were hit. I cannot say the same for my 7mm Mag even on great hits. Not sure why but years ago I read an article on sectional density and it makes some sense.

The only down side I saw on my Remington was that the barrel was so light that if you put too many bullets through it the impact point would start to drift as the barrel heated up. But out to 200 yards it is as good a deer gun as any others and I think 300 is not out of range either although I never have shot out that far at a deer but I think the ballistics hold up out that far.

You will not be disappointed.