We all know he's a natural Lightweight (135 lber) fighting at 147, nothing besides his calves are big. Hell, even a 29 year old Pac would clean out 147, let alone a bigger version. Would anyone in the Welterweight division even go near him? I think he would body the whole division.
Giving Pac 2 more inches in height and 2-3 more inches in reach isn't going to result in much loss in speed. That said, a 5' 7" and a 69-70" reach Pac would be even more of a killer.
...he would be a completely different fighter. He would have completely different timing, different leverage, different angles. Tall height doesn't favor the sort of offensive motor Pac has (chin up and wide all fight).
With all things considered the same but at that size we`d be talking about unquestionably the GOAT and FlIVd would never have fought him.