Originally Posted by OTMPut
There lies the fallacy.
The improvement from switching from 90 to 95 is significant for an average club player. The less accomplished, the more is the relative improvement.
At Fed's level there is little he could improve. It might reduce his shank % by say 5 to 10. He would also lose elsewhere -feel, control (esp with his whippy wristy forehand). He might put more balls into play from his backhand side. That does not mean he would automatically win those points. It is not a straightforward sweet spot math.
I am sure he is smart enough to weigh up positives & negatives. Apparently he switched from 85 to 90 once. I am sure he would again if he think that would make a positive contribution.
Wilson Asian K90's 343 grams/32.5 cm balance/335 SW. BB Ace 18 @ 63#. Frames matched and identically strung by 1stServiceTennis.com