What is the recommended pressure for refueling an Airbus A380?
The A380 airport planning manual states (emphasis mine):


  Refuel pressure:
  - Maximum pressure: 50 psi (3.45 bar).


Can it be safely increased? Doubtful. Any increase may damage internal aircraft systems, and not only that, the operators will need to ask the airports to install new refueling systems.

Generally:


  For pressure refueling, a high-pressure hose is attached and fuel is pumped in at 275 kilopascals (40 psi) and a maximum of 310 kilopascals (45 psi) for most commercial aircraft. Pressure for military aircraft, especially fighters, ranges up to 415 kilopascals (60 psi).


As for the rate, from the graphic and the text:


  
  
  242 700 l (64 115 US gal) at 40 psig.


242,700 l take 36 minutes, or ~6,700 l/min.