Prime Fed yes but Old Fed has become susceptible to being hit off the court by big hitting ballbashers (the type of player who he used to chew up and spit out) at grand slams- I think the likes of Tsonga would love a fast court against Old Fed.
against Tsonga probably because of Tsonga's serve (but it was also true for prime Fed, not only for the old one), and still not sure because Tsonga would struggle to return Fed's serve on a quick court and he has more concentration lapses than Fed to lose his serve, but not against the other "big hitters" :
against them, a fast court is better for Fed to move them around.
Besides, even against Tsonga, it was visible last week that Tsonga had enough power to generate his own power through cold slow conditions whereas old Fed didn't have that power.
Fed prefers when the ball goes more easily through the air, esp. in his old age : in his young age, he had more energy to generate his own rhythm.
Maybe one could say that slow courts are not bad for old Fed, but slow balls are.
In Miami damp conditions, and in cold conditions on AO plexicushion, he's completely powerless.
On clay with light balls, he's much better.