Federal 210 M seem to work best for me when using bullets up to 147 grains. Then it seems like the 215 will produce tighter groups with the heavies in the 6.5 class and slower powder and 1:7.5 twist barrels.
Magnum if you plan to use this in cold weather. It has superior ignition to ensure proper powder burn. Especially on cases that use a lot of powder. In low case volume like Creedmoor no need for magnum