Reloders nest is showing 221FB velocities of the 55gr bullets up to 3300fps using H4198. Thats just as fast as the 223 with a 55gr bullets.
I don't believe for a minute that a .221 FireBall will shoot a 55g bullet as fast as a .223 out the same length barrel with both loaded for max velocity and within pressure limits regardless of what it says on Reloaders Nest.
It's the same brass where it counts, in the base so it has the same peak pressure determined by the brass strength in the base. Case capacity of 22 water grains for .221 FireBall vs 28.8 in the .223 (SAAMI) or 30.49g which is what my CZ .223 has. That means there is 31% to 40% more powder in the .223Rem. than the .221 FireBall. That powder difference isn't going to be made up by magic in the .221 cartridge. Just plain isn't going to happen.
I tried to get there, closest I could get with powder that would fit in the case was H110 @ ~89,000 psi in a 55,000 psi case. Nope, not gonna happen until sombody repeals the laws of thermodynamics.
Estimating an answer to your other question, in QuickLoad your 17" .221 Fireball looks like it's good for ~2,600 to 2,700 fps with a 55g bullet. The best domestic powder was RE10X which came out at 2,629 fps in a 17" barrel at max load. PBR of around 194 yards
For comparison purposes:
A 55g .223 Rem loaded for my CZ is predicted to have 2994 fps out of a 17" barrel.
A 55g out of a 17" barrel 6x45mm (6-223) is predicted to have a MV of 3,114 fps. With more bore area and the same pressures a .243 bullet goes faster than a .224 bullet of the same weight. Essentially the same PBR as the .223 or ~214 yards.