What should I set my fuel pressure to?

40psi

38

lean is mean NA

Its about 40psi stock.

My friend has the stock regulator and it shows 45 with the vacuum line off and plugged. Dunno wtf is going on with it, odd.

Use the SOP meter...

Get one of your buddies to ride along with you. Find a level stretch of road where you can do some testing. Don't choose a speed range that will make you shift gears, the shift quality & speed will affect your results. Use 2nd or 3rd gear and do a run from 2000 RPM to 5800 RPM. Call out the RPM as it increases and have you buddy record it and the elapsed time. If you have one of those cheap digital watches like I do, a stop watch is built in. Start the fuel pressure at 36 PSI, vacuum off and make a run. Turn it up to 37 and make another. Be sure to reconnect the vacuum every time you set the pressure. Keep turning up the pressure and making runs until you notice a drop off in time. If your bud was careful to record the results, you'll have a nice chart to use to find the optimum pressure.

Note that you should travel the same direction each run. The wind direction can have a great effect on the results. A 5 MPH headwind is a gentle breeze, but it could throw you results off by quite a bit.

Run 39-41psi with the vaccum line off and plugged with some tap or your finger. Set it at idle when warm. Turning the stud clockwise sets the fuel pressure up and counterclockwise drops the fuel pressure psi...

Jrichker is right on with the differences in where you do your SOTP testing. Make sure it is the same strip of road in the same direction. The test can help but your going to need some sort of consistency with your timing of pushing the "ticker". I would make increments of a few lbs to make a more noticeable difference so you can get a better estimate of the right ballpark to be in. Fine tune from there...Good Luck