I ran for a year without a fuel pressure gauge. With a TST box and not getting too crazy I didn't think I had a problem. The truck ran well. I decided to put on an FP gauge and was surprised to see 5-7lbs. at idle and near zero when I leaned on her. A few days later, I installed a FASS11. I now idle at 18lbs and pull it down very little under heavy throttle.
To answer your question: You probably won't know until you put a gauge on. Good luck.