I ran mine all weekend - both were whisper quiet. Ram pressure is set at 75 psi on both markers. I wouldn't be focused on making the operating pressure "super low". It's a balance between PNreg, and the Sidewinder, as you've found out this weekend.
That being said, my HPR is running around 160-170psi, and that's getting me in the 270's for fps - with no ball breaks.
Good luck with the Excal!
"You can get more with a kind word and a gun than you can with a kind word alone. "
- Al Capone (1899-1947)