Be careful about the number of bends on the duct as well but, a 3" should do it as long as the bends are sweeping or no more the 3 90 degrees.

100%....pull a flexi-pipe inside the 3" for the fibre for protection. If you do this, ask the customer for a 4" because the pipe will take up much more room than the fibre so, it will leave you will additional room to pull another cable if you need to for re-inforcement, repair, etc.