In particular I’d say “did unpublished research on topic X” sounds like “did research that might be published (i.e. is valuable and original)” whereas “researched topic X” sounds more like “read about things.”
In particular I’d say “did unpublished research on topic X” sounds like “did research that might be published (i.e. is valuable and original)” whereas “researched topic X” sounds more like “read about things.”