I have the PB4+Slide copier setup and have done some capture of slides to negatives. What information are you looking for exactly - how much resolution and color fidelity can you capture?
I also sent some slides to Fuji and they gave me internegs. This wasn't my intention but back then (1990's), in order to get 2" X 30" prints from slides, Fuji would first make an interneg then optically print from it. I'm not sure if they still do this.