I've tested it. Using the same provided brick with the Note 3 - 5.3v 2.0A, the supplied USB 3.0 charges exactly the same as the USB 2.0 cord supplied with the S4 when plugged into the wall (1200mAh).
The only time USB "CHARGES" faster is shown below, tested:
-USB 3.0 + USB 3.0 port on computer = 1A.
-USB 3.0 + USB 2.0 port on computer = 0.5A.
-USB 2.0 + USB 3.0 port on computer = 0.5A.
-USB 2.0 + USB 2.0 port on computer = 0.5A.
Again, the only CLEAR advantage to the USB 3.0 cable is when transferring files off a USB 3.0 equipped computer; it does it much quicker.
The only time USB "CHARGES" faster is shown below, tested:
-USB 3.0 + USB 3.0 port on computer = 1A.
-USB 3.0 + USB 2.0 port on computer = 0.5A.
-USB 2.0 + USB 3.0 port on computer = 0.5A.
-USB 2.0 + USB 2.0 port on computer = 0.5A.
Again, the only CLEAR advantage to the USB 3.0 cable is when transferring files off a USB 3.0 equipped computer; it does it much quicker.