Pass Labs - X250 VS X250.5 VS X250.8


How big of a difference is there actually between each each of these amplifiers? I've been looking into Pass Labs gear recently, and the price difference between these pieces on the used market is huge. Is it worth spending thousands more the .8 over the .5 or the .5 over the standard X250? etc. All advice is appreciated.

Thanks!
nemesis1218