In any weight class. for instance, i think Mayweather and Jones woudl do very well vs. their p4p legends. Vitali could do well in heavyweights (or super heavy) Hopkins too
I think Jones would struggle against legends with great jabs who could cut the ring off, Griffin backed Jones into the ropes and outworked him in their first fight he and Futch spotted this weakness in Jones during the McCallum fight, a prime McCallum would have beaten Jones at middleweight during his era I feel but Hopkins would do much better.
Bob Fitzsimmons, Stanley Ketchel, George Dixon, Young Griffo, Jack Nonpareil Dempsey, Philadelphia Jack O'Brien, James Jefferies, Jack Johnson.
I guess you mean this past era since those guys are all retired. Prime Shane and Oscar could beat some ATG Welterweights on their day.