Start with around 35-40 psi, 4-5 mph, and figure to use 25-30 gallons per acre. Go out and spray a known acreage to test your settings, then once you have fine tuned a combination that seems to work well for you, write it on your sprayer tank and always use the same settings.
I use a label maker and put my settings on the tank right beside the pressure gauge.
Start fine tuning with your preferred gear, it's possible to spray at high speeds, but the rig and booms tend to bounce a lot if you are going too fast, so find a gear that you are comfortable with, then use the pressure to increase or decrease the gallons per acre being applied.
I just sprayed my 4 acres of beans at 4mph, 30' booms, 35 psi, 30 gallons per acre. On the last round I decided that my product wasn't going to reach, so I cut back to 30 psi, then I ended up with 5 gallons left over