Best long range caliber?

The best long range rifle is always going to be a compromise. You just have to be sure it is your compromise. 

Generally, the more muzzle energy you pack into a pellet the better it is for long range.Since pellets lose their accuracy as velocity reaches a point in the 900s or there abouts. The only way to increase energy is to use a heavier pellet. This favors larger calibers. 

Sometimes tactics outweigh power. A common time limit for airgun benchrest is 20 minutes for 25 record shots. I prefer to shoot the entire match on one fill, because any time I am filling the gun is time that my condition might return and that is when I should be shooting. So that in a minimum of 25 shots. If a .30 can do that OK.

My choise is a .25 bottle gun. 

If I may, I have two suggestions. First spent the extra money for .30 on a good set of wind flags. I don’t have a set and my scores suffer for it. Second start shooting your .22 at 75 now. Only experience will make you a good long range shot. 

I hope I see you at EBR.

Ron