[Chip & Charge]

Also here are their serving stats, Federer's are superior as you would expect:

Fed:
Aces per match - 8.47
Double Faults per match - 1.57
Differential per match - 6.9

Djok:
Aces per match - 5.42
Double Faults per match - 1.79
Differential per match - 3.63

So in 2012 Federer gets nearly twice as many free points on serve per match