At this point 6mm CM is looking pretty solid along with what seems like an endless number of other options...
If you are talking about the 6mm Competition Match I think that would be a really nice cartridge choice among the others mentioned here, except they are getting 4000 rounds of barrel life, mainly due to a slightly larger case to get enough slower burning h-1000 in the case. Otherwise, if you are talking about the 6mm Creedmore, it doesn't seem to have any advantage over the others.
From what I understand of Joe Hendricks design, it is more about using a slow burning powder and using JB bore bright to burnish the throat often, regardless of the case.
That being said, the .220 swift AI with 80 grain bullets seems like a pretty good step to save you money and if you can use as cool burning powder as possible you might increase barrel life.