You can use an XFULL tube with buckshot if you want, but I wouldn't. Might not hurt a thing, but it isn't a chance I see the need to take, or even see any reason to take. And what about shooting slugs through that choke tube? Is that a consideration for you?
With buckshot, beyond a certain point, more choke might well work to OPEN patterns, not tighten them. It takes patterning to find out what does what with a given shotgun barrel, and every barrel will pattern differently. Only way to know what a given load will do in a given barrel is to pattern it. That means one shot at a time on one patterning board, in my book.
It is possible to get buckshot on targets at 100 yards to a degree, several years ago I was getting 20-30% patterns of the then available (pre-FliteControl) Federal Premium 3" 000 buck loads on GI E-type silhouettes at 100 yards using a Patternmaster choke tube. This tube was a wad-retarding choke that was essentially CYL bore... but it wasn't recommended for use with slugs, so it was a dead end as a general utility approach to extending shotgun range for me.