been loading 260 for about a year.  love the cartridge.   i've had no issues finding primers or brass or projectiles.     just the h4350 powder everyone rants and raves about.

i've found other powders instead

Ballistically they are basically identical. You might get 50fps more in a .260 but I doubt much more unless you have a fast barrel. It comes down to OAL and factory ammo availability. The Creedmoor can be loaded shorter to fit easier into mags especially semis. You can also find more abundant and cheaper factory ammo for the Creedmoor especially match grade. Remington dropped the ball big time with the .260 not offering good match ammo or rifles. A lot of options in rifle and ammo for the Creedmoor now as the companies picked up that ball Remington dropped and ran with it in the way of the Creedmoor.

It used to be said that the .260 was for handloaders, mainly due to Lapua brass, and the Creedmoor for people who wanted to use factory ammo but with the larger amounts of companies producing brass for the Creedmoor, even Lapua, there is no difference anymore. They both use the same powders and bullets.