There are plenty of moose that get shot with a 6.5x55. Your creedmoor will do fine. It's largely down to projectile choice.
If you're dead set on getting a different caliber there is no point in going with something that is similar in energy etc, eg .308, 7mm08. You might as well go with a magnum or similar. And these days you have plenty of superb options, stuff the 7mm rem mag or .300, go with a 7mm PRC and spit those big high bc pills out at a decent velocity, even out of a 20" tube.
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