I have a few FX airguns and different barrels/calibers for each. Some can be a pain to swap calibers, but one is really very easy. The M4 Impact can be swapped in a matter of minutes. Just 2 grub screws, one for the barrel, one for the probe and you're done. Tuning to a new caliber is very easy as well, just a quick adjustment of the power wheel and valve adjuster and you can go from .22 to .30. I have 3 barrels, the .22, .25 and .30 all 600mm and actually change them more than any other FX I have.
The Edgun Leshiy's, especially the II's, are on my dream list, but out of my budget, as are the Impacts. I was looking more at Dreamline price levels. The Avenge-X might also be a caliber swapable option.