I'm not sure what discipline you are referring to, but I would beg to differ that the 6XC is a little light for 115 grain bullets. David Tubb shot a "clean" (800 out of 800) and won the Canadian Cup with his 6XC and 115 DTACs at the Long Range Nationals last year. A lot of people (including me) are running the 115 DTACs between 3000-3100 fps in 30-32" barrels. Could you let us know more aboutting what you are trying to accomplish, or are you simply trying to understand why the 6mm CreedMOOR is apparently more popular than 6XC?
I have a buddy shooting 6CM and I'm shooting 6XC. I"m shooting 115s and he's shooting 105s...But he has 200fps+ muzzle velocity advantage on me. I'm thinking of building one. Maybe I'm just not putting enough powder in mine but I'm shooting 2950 fps at 39.7 gn of 4350. Another buddy shooting 6xc went after a faster node and 400 rounds later he is back at 39.7 with me. So the 2 grains of water may be attractive to me. I'm getting a new stock back later this month and will either bed my 6xc into it or build a new rifle and 6CM is the leading candidate.
I'm also considering trying 6SLR again but to me the key to selecting what to build is what brass to use. I wasn't happy with my brass options for the SLR the first time. That said, it shot very well for 200 rounds, then I overheated it in a 1000 yard match with an idiot in the pits and it was never the same. I may try it with Lapua brass, even though it is usually recommended using a "cheap" brass like Rem or Win that reforms easier into the SLR shape.
If I do build a 6CM, I plan to make it .010" long and rename it. You'll hear me talking about the 6JLS (my initials).
--Jerry
Bob3700 - In my experience, the new Peterson SRP 6XC brass (available from Tubb) allows for hotter loads without showing pressure signs than the Norma ever did. If you haven't tried it yet, you might consider doing so, but it sounds like you've already made up your mind.
I also have a 6SLR (using neck-turned Lapua brass since Rem and Win were both disappointing) and shot the 115 DTACs, but have since switched back to the 6XC with Peterson brass since it performed so much better for me than the Norma 6XC ever did and performs close to the 6 SLR in an easier to manage configuration (for me at least - no neck turning or fire forming).
I am only seeking to provide my personal experience as another data point for you to consider, especially with regard to the latest version of the Peterson SRP brass which has only recently become available.
The 6CM has a water volume of 50 grains and the 6XC was a water volume of 48 grains.