User blog comment:DirgeOfCerberus111/Adeptus Custodes Vs. Grey Knights/@comment-1536954-20110819112502/@comment-1932673-20110819170737

None of which would be especially useful against the Custodes, who are non-psykers and have spent most of their time close to the Emperor that would probaly have some sort of side affect which would neutralise the special effects of GK weapons, meaning any contest would be one of brawn, which Custodes wpuld win, due to superior genetic conditioning and numbers. Not to mention if the GK and Custodes were at war, the larger Imperium would stand with the Emperor's bodyguards anyday.