I know I'm responding to someone who posted in January who was responding to someone a couple years ago...
But the .260 is going to be way more popular than the 6.5 CM in 2/4/8/10 years. It is the .308 necked down, has better factory brass availability (Lapua/Nosler/Remington/Norma/Federal), and target shooters are buying them like hotcakes.
If/when Federal comes out with a GMM load for .260 it will sound the death knell for the other target 6.5's. They will stay around forever, as target shooters are a picky bunch and don't mind playing with odd calibers, but the train will have left the station.
The 6.5 CM will go the way of the .30 TC - great cartridge, but can't compete with the .308 family.