What under-performing 6 ARC or 243win loads are you considering when you make the misguided claim that both will be sub-sonic around 700yrds? Either of them will hang onto super-sonic speeds beyond 1000 yards.

The comparison here is much simpler than all of this. Whatever the 243win has done for decades, the 6 ARC does 500fps slower.

Interesting that you also chose to neglect to mention in your reloading section that two pressure standards exist for the 6 ARC, one for gas guns limited at 52,000psi, with the bolt gun pressure standard increased to 62,000psi, adding ~200fps to the ARC’s performance from an AR-15.

Pretty simple to see the performance difference between 6 ARC, left, and 243win, right.