Jimmy Connors would get handly defeated in todays game by Federer. The increase racquet speed means that he like all the short players without devistating John isner/milos Raonic level serves would be unable to play serve and volley type games. They would be playing a baseline game where footspeed is one of the key elements.
Jimmy Connors height is a factor in why his serve wouldn't be in the top 4. So he couldn't play his serve and volley style game. He wouldn't be putting his opponent on the defensive enough nor pulling Federer into vulnerable positions on court with that serve to safely move into the net without getting passed by Fed.
Jimmy was only 150lbs, even with good angles he wouldn't be hitting flat backhand balls with the same penetration as players like Djokovic or Nadal, nor with the high bounce topspin that troubles Fed.
If both players have their A game on in their prime.
Fed in 3 or 4 sets. 6-4, 6-4, 7-5 or 6-4, 4-6, 6-4, 6-3.