@ Tyropicard: Probably not what initial poster was looking for...
I guess he is looking for the maximum permissible GS-deviation during approach (right?!)!
I was recently discussing the same issue with my captain. Our manual states the maximum allowed discrepancies for CAT II/III, but nothing mentioned about CAT I!
My pov: if you stay within the limitations, obey SOPs and are established according to the books, no problem to deviate from the glideslope (to fly above, NOT below the GS) in fair weather. Different thing under "real" Cat I conditions with RVR less than 800m...
Sorry - but i canīt give you a more precise answer, but looking forward to other comments!
Cheers