I can't find it but recently (within the last week) there was an article (HN, Ars, reddit??) about a new record of about 768 Tbps (not Gbps) but real world about 650Tbsp. It used different colours/wavelengths of light, 23 or 43, and did some frequency alteration plus kept most of the overhead at the source not via repeaters.

So yeah the roughly 650Tbps seems usable in such a situation.