Different bore sizes and choke systems 425 through 625 uses Ivector plus 725/825 have oversized bores with the Invector DS choke system
Ported non ported bbl's
725/825 have different triggers I prefer my 725's triggers over older citoris
Different stocks , forend styles Checkering , engraving Palm swells etc
Basically the Evolution on the Citori in successive numbers . All made by Miroku so "quality" could be a subjective personal thing.