I'm building also a Caad5 - r900si (in a dark blue to light blue faded colour), and is 52 seat tube / 54 top tube (c-t-c),
i've bought a 90mm, but not sure if it is too short, as i'm also +/- 5'10
Yes, there is allready a washer, but even with the washer there is some play,
will try to film it today, just to understand if the amount of play is ok, or too much.
What frame is this?