It may or may not matter. The extra velocity may stabilize a particular bullet better than a shorter and slower barrel will. I guess that it would depend on what is meant by the word "matters" in the statement above.
Does an inch or two matter?
Does a better group matter?
Does better penetration matter?
Does up to a 5.5% increase in velocity and penetration matter?
It could matter in competitions like those being held at Friendship, Indiana next month.
A precise velocity sure does matter to an Olympic shooter who is trying to hit the X with every shot using super expensive ammo which a gun may be harmonically in tune to a particular higher velocity.
IMO it can't be reasonably predicted that the increase in velocity won't matter
It can at least be said that the barrel offers a wider range of velocity options for custom tuning the gun to a particular bullet.
The actual benefit in performance may not have even been discovered yet. And that's just with Blackhorn, there are other powders too.