Hi Skeeter, I was with a youngster in Kansas this year when he dropped a 320 lb white tail. I called him in using a rattle bag to our bale blind. He was 320 yards, he was hit dead center of the shoulder on a broadside shot with a 100g Hornady SPBT going 2950 fps. The bullet broke the shoulder on the side where it entered and destroyed the heart and part of the lungs with no exit. He traveled 20 yards after being hit.
I do believe that this shot is about the limit of the effective range of the 243 to say the least. We had spent a lot of time with this particular rifle and knew of it's capability at 300-400 yards. The bullet's construction was adequate, but the core ran out of gas on the first shoulder.
You can not count on getting a broadside shot all the time, you have to take the best shot presented...that's hunting for you.
I had a hunting partner use the 85g Barnes Tripple shock. He shot a doe at 85 yards as the doe was going away from him. He shot the doe in the right hind quarter, slightly quartering, so the bullet would angle through the body and possibly break the shoulder on the diagonal. The bullet did in fact break the shoulder and exited. The deer of course did in fact drop in it's tracks. The 85g Barnes Tripple shock is VERY accurate in his 700 Varmint.
The Barnes 85g may be an alternative for you on a good deer bullet. The Barnes Tripple shock bullets that I have shot in my 7 Mag have been very accurate and do not copper foul anymore than a normal Nosler Bullet.
Good luck to you!