CHEMISTRY ALERT! Yeah, both Sid and JJ are first line players, but so were Hull and Mikita, and they played on different lines because they each wanted the puck so often. Same here. Messier played with Gretzky early but it became quickly apparent the team was better with each anchoring their own lines. Many of the best teams of different eras had a superstar on each of the top two lines.
Crosby and Jagr should each be the playmakers of their own line; Firsov was known as selfless, hard working and skilled one on one, so perhaps put Firsov with Crosby; Sittler was known for his wrist shot and toughness, so he and Jagr ought to click. Hence, the advice is to assemble two balanced high octane lines, 1 and 1A:
Firsov - Crosby - RW
LW - Sittler - Jagr