I'm a big 243 fan. The 6 Creed, and 6mm, are pretty much equals, IMO. You MAY eek out 100 fps more than the243 with either of those cartridges, but 50fps is more like it. For the added cost of brass, the juice isn't worth the squeeze, IMO.

For the guys shooting factory ammo, yeah, the 6Creed wins, better ammo selection for long range.
And, there seems to be more off the shelf, long range type, rifles chambered in the Creeds.

IF I were building or rebarrelling, 243 every time.
By the same token, I'd go 260 Rem over 6.5 Creed, or 6.5-284.