So there are two implicit questions here you're actually asking. The first is the angular MOA of of the Crown in different calibers, and the second is environmental effects.
So the actual angular MOA capability, in general not just on the Crown, I've never seen any definitive evidence that .25 is more accurate than .22. With calm air, I can print sub MOA 10 round groups at 100 yards using my crown in .22 and JSB 18.13s. I haven't run it in .25 to compare, but even given the glory shots a lot of guys are posting here, I don't see anything to suggest that the .25 is radically better. Hypothetically it could be a little more resistant to minor defects, but theory and reality aren't necessarily the same.
The reason why you see the "common knowledge" that .25 is better is because the 33.59 grain JSBs have excellent ballistics and have traditionally been seen as having less wind drift. The advent of the 25.39 grain .22 redesigned pellets may well change that. I have not seen a back to back comparison to test. The apples to oranges of EBR suggests that people have gotten .30s, .25s, and .22s to all essentially be competitive with each other.
And this all ignores the potential for slug conversions, which promises even better performance at long range.
But, something to keep in mind, I run a bullseye target with a 3" center. I can, with my .22 Crown and JSB 18.13s, go out to 200 yards, and go ring that little circle. I've done it on challenging breezy days with swirling shifting winds as only New England seems to be able to produce. This is clearly not the "optimized" setup, but it is only a target, and I enjoy the challenge of learning from the wind. So honestly, I'd say for target shooting just don't sweat it too much. Get the caliber you like. The gun can be converted if you change your mind later, or as a better liner/pellet/etc comes out in some other caliber. There is a lot of chasing "the best of the moment" in airgunning, and real progress has been made, but it is important to remember that tomorrow there will be some new hotness. I think of the real edge of the Crown is that, of all the guns out there, it (along with the Impact) are best inoculated against advancing technology. A new amazing pellet, a better intermediate caliber, whatever it is in theory the Crown will get a conversion product. *shrug* At the end of the day though, I try not to get too worked up in whatever the latest is. Take a deep breath, shoot what you like, and enjoy it. That is what its all about.
