I think it's 260 Rem, which is why I built one. But be realistic about the benefits vs cost of rebuilding your existing rifle. If you already have a 308, you might not gain anything - and may lose overall - by changing it.
With that said, 243 Win or AI with fast 115 DTAC bullets beats the 260 on paper. Depends what you're willing to compromise on - barrel life, paper or animals, factory ammo or reloads, recoil, brass availability, etc.