Don't understand why anyone would convert to fiber at end of chain, converting to fiber should be done at beginning of chain. Cheap fiber converters certainly not optimal, and transceivers do make a difference, industrial grade Finisar 1475 was my choice after trying others. Corning optical cable top level, I use After Dark version. If your going to do fiber conversion cheaping out will result in second class performance.
What comes prior to fiber conversion matters greatly, fiber can't bring back what's lost prior to the conversion. Where ethernet remains, isolation and quality ethernet cable a must, entire chain must be optimized.