A review of the loads used by the champions using the 6.5 Creed indicates that most use H4350. That means you should probably start with 4350 and work up a load that works. Every rifle is different, so it is common to find variations of up to a full gr from rifle to rifle.
As for a factory, they typically load to a a specific velocity, so load the powder required to get that velocity. The powder choice might always be h4350, for example, but the actual charge will vary from powder lot to powder lot. The non-canister flavors of h4350 vary in speed.
In other calibers the factories also load to velocity, but don't much care which powder they use. Many powders will deliver 2750fps with a 180gr bullet in 30-06. They use the powder that they can get in sufficient quantity for that particular task.
If you use factory ammo and you happen to have a box of ammo that is outstanding, note the Lot# and go buy some more. Because the next lot could be very different.