Well the WDP regs arent the highest flowing in the world.
So to get a good concistent output, it is best to have as high a pressure input as you can.
When you set the gun up correctly, you should need about 250 - 300 psi to run the gun, which is perfectly attainable with a stock reg and HP output air system.
Good settings depend on the gun and its condition, the board, any mods etc. But a good place to start is: dwell 8-10, LPR 70.
Even on the newer angels, people often try to get lower pressures by having ridiculously high dwell values and really low LPR. But that gives you a gun that isnt very concistent and loses accuracy completely when you shoot more than 4bps.