I've never killed an elk with a 243 but I have several friends who have and I know others who've used a 6mm Remington - and I'm talking about neat kills, not rodeos. It's all about shot placement.

I killed a big mule deer buck the season before last with a 105 Hornady HPBT from a fast twist 243. It was a pretty severe test of that bullet as the buck was very heavy and he was only 5 paces away so impact was pretty close to muzzle velocity. It worked great and I may carry that combo again if I can arrange a cow hunt this fall.

6mm monolithics will work. Partitions and 100 grain Interlocks are other 10 twist options I wouldn't hesitate to use.

The 6.5 Creed and 7-08 are also great modest recoil options too if you want a new project.

"The trouble ain't that there is too many fools, but that lightening ain't distributed right." - Mark Twain