I have a Gucci belt fanatic, for me the best length would be if it fit on the/a middle hole. It is short, but it's your pref ;-)
Its a bit strange.. I have always used 85, and this is a 85. I also use the same hole on this belt as on all my other 85 belts (not the middel, but the second hole). -but the lenght of this belt is couple of cm shorter. It's also a bit shorter than the other Gucci belt I bought in 85. I still think size 90 may have been too long.