mine was in a Medium (chestnut in sig) and she was full Irish TB 16.1hh - i'm sure you could get a TB in a wide - but not sure about x-wide... but anything goes with horses!!
Hum. Saddler (master!) was convinced he couldn't be full TB. He doesn't have prominent withers, if anything he is quite flat-backed. He said the muscle build and back shape is all wrong...
His Stubben wide jump saddle is too tight for him, he's in a walsall now but they come in a whole range of sizings so I'm not sure exactly what he is, Sayer said somewhere inbetween W - XW. He's only 16hh, btw.