The challenge with this stat is that Fed going five sets at all means he's not playing that well. At his peak, he'd just wipe people out in straight sets, four sets if they were playing really well. That he had to go five showed he already wasn't at his best (with some exceptions such as the Rome final against Nadal). Also, serve is good in tiebreaks, but it's not everything. That's why Fed, Novak and Rafa can beat the big servers in tiebreaks.