243/6mm would be damn cool. I really like my 6x45 and also my 6WOA. Those were/are AR15 platform, but performed very well. The 243 or 6mm Creed would be about perfect with a fast twist barrel. I have to reiterriate the 6.5 cm though because I've only had the 308win and it to compare. In my experience the 6.5 is head and shoulders above the 308w. That may just be my 2 samples though, but I have not been convinced otherwise by other AR shooters. The 6.5 CM I have walks all over the others I've seen. Its a true sub moa shooter. The 308 I have is a true 1.6 moa shooter. The creedmoor is gentler on the shoulder and quicker on target for subsequent shots. The rifles I have are not braked, although when I had a muzzle brake on my creedmoor, recoil was reduced substantially. As it would be for the 308w. From what I have seen, the 6.5 cm bests the 308 in the accuracy department, almost without even trying.. Those that want to argue, can post up targets and we can compare.. That's always fun..
