The Webley side levers often struggle to make "full power" in the more efficient .22 calibre (even the Tracker/Viscount with its more efficient transfer port), so converting to the less efficient .25 is not a good idea.
The Vulcan on the other hand, with its easily changed barrel, is a better option. It has more swept volume, and being a breakbarrel with less energy loss than the tap loader makes it a better option.
Plus it is easy to convert back if you change your mind.