Making wildcats is fun with guns.
On the practical side a 243 will be easier to find and get.
Also the 243 can be loaded down to near a 6BR.
Just presenting an alternative. A 243 Kimber Montana weighs just 6#,11oz. with a 4.5-14 Conquest on it. Thats what a M70 Featherweight goes without a scope!
The 243's ammo is available everywhere. You will never find 6Br loads for game anywhere.