Bizzmo is your 6 Creed rifle a single-shot and so throated or is the reamer used for it set-up for a magazine?
All things being equal (which they rarely are), the larger case capacity, when you can use the full capacity (Like in a single-shot) where you can throat long depending on the case the larger capacity is going to out perform the smaller one with heavy for caliber bullets. This is also assuming the same/similar pressure.
I have a 308 Winchester rifle (Yes, I said rifle) that runs a 200 grain bullet at 2626 fps, and I could run it faster, but it shoots so stupid good and stays in tune with 42.0 grains of Varget, there is no reason to run it harder, especially when running 20 round plus strings.
I promise you it would not be wise to try to do the same thing with my Remington 700 rifle (20" barrel) with my magazine fed 165 AB's(2580 fps). Or in a another guys 308 using a mag, 168's at 2721 fps (24" rifle). Sticking a 200 grain Berger 200.20x in either rifle that uses mags would be kind of silly. The other disparity is the barrel length of the two. Plus my F-TR rifle is a single shot action and so throated.