There wasn't a 168 division back in his day. Bob is most known for his move from middleweight to heavyweight and winning a title. I personally think ANY elite heavyweight would easily beat fitz, which is why the question ends at 175. What fighters do you favor over him from middleweight to light heavyweight? Discuss.
I wouldnt put the house on it, if i were you. If forced to pick a contemporary who did (or would) beat Bob Fitzsimmons, I think Mick Dooley would be the better pick. Mick only really seemed to win a no decision 4 rounder (or two) but i do think that their was a period of time where he might have been a reasonable chance to win a prize fight.