If you use the 105gr Bergers in the 243 and find the highest velocity node your gun will allow, they will offer plenty of downrange energy. I have been surprised that the 105 and even 95gr VLD's penetrate half way through a 1/2" piece of 410 stainless steel plate at 300 yards. They make a much deeper impression than a 175gr SMK at the same range from my 308.
As others have said, shot placement is key. I don't believe there is a bullet out there that can compensate for a bad hit. Once you have a good hit, I personally doubt that 1 bullet vs another is really going to have a substantial effect on the outcome. Now if you are facing down an elephant/Cape buffalo at 30 ft, I might want to have the best bullets money can buy but most of us will never be in that situation.