As for the 6mm Creedmore "what the pros use" see article with all the details including the graph that sable tireur used.
6mm Creedmoor | PrecisionRifleBlog.com
I read the entire thread on what cartridges are popular. It is the PRS (Precision Rifle Series) which is a specific type of competition which doesn't necessarily coincide with the OP's needs.
I can't imagine using Hornady's brass for a cartridge when Lapua brass is available.
Regarding the 6 CM: Found this quote: "There are a few quirks of setting up a 6CM: 4-groove barrels and a .237" bore seem to be very important. Joe Hendricks, the cartridge designer, has said that the only trouble barrels he's had have been .236" bores and/or 5-groove barrels. I had trouble with a .236" bore, and putting on a .237 fixed it. However, if you go with a .237" bore 4-groove, then the guns do not tend to be finicky at all about the loads. (I've had 100-9X or better at 600 with 4 different loads with three different bullets, including the fireforming load mentioned earlier)"
------------------------
I would choose the 6 x 47.
The 6mm-6.5 x 47 Lapua seems like a better platform. Lapua brass with small primer. Some fantastic articles on it:
6-6.5x47 Lapua Varmint Hunter
Beginski's New 6mm-6.5x47 Lapua
----------------------
I have been looking at the many 6mm variants out there. I have decided to have a 6 BR reamer made. . Not too long ago I took my 30 Br reamer and went 1/2" deeper to make a 308 with a 30 BR neck, 30 degree shoulder and 30BR body taper. I bumped into something very similar in 6mm called a 6mm BR-K. I believe I can make a very similar cartridge by going 1/2" deeper with the 6 BR reamer. The beauty of this is being able to use a 6 BR die set for both cartridges.
Information on this 6mm variant:
Gunsmith Mike Sosenko and long-time AccurateShooter Forum member John Adams have been using a modified .243 Winchester case with great success in Varmint Silhouette matches at the Pala Range in Southern California. Officially called the ".243 BR-K" (and informally dubbed the "6BR Long"), the wildcat is basically a .243 Winchester with less body taper and a 30-degree shoulder. The design essentially grafts a 6mmBR Norma "top end" to the .243 Winchester case. After fire-forming, Mike and John can reload this case using normal, unmodified 6BR neck-sizing and seater dies.
Compared to a .243 Winchester, the .243 BR-K's body length is about .006″ longer, and the shoulder is about .0055″ wider. The main difference is the shoulder angle (30° vs. 20°), and the location of the neck-shoulder junction ("NSJ"). Based on reamer prints, the base to NSJ dimension is 1.718″ on the 6BR Long, compared to 1.804″ for the .243 Winchester. Neck length is a bit shorter because "the neck shrinks a little when the shoulder blows out" according to Sosenko. You can check with Dave Kiff of Pacific Tool & Gauge for exact dimensions. Dave created the reamers for both the 6mm and 22-caliber versions of this wildcat. Ask for the "22 BR-K" or ".243 BR-K" reamer designs.
So many chamberings so little time.
Enjoy the process.