I've seen very similar motors like different fp's. I started at 45 and worked down. Think I ended up around 40, but another friend's car ran best around 35. We just went by trak times (mostly mph) to set them.
Ok, I just installed a SCT Chip and the instructions said to set the f/p at 39 vac off to start. It was set way higher from the intial tune I had done last summer, 49 vac off. It seems to run a lot better now on the lower pressure. Will playing with the f/p give you decent gains or is it just driveability?
At WOT the PCM uses fuel corrections learned at part throttle to compensate. If the fuel pressure is too high or low the correction may not be right at WOT, only a WB02 can determine that. In closed loop the PCM can adjust +/-15% or so to make up for minor inaccuracies. The PCM also assumes that the MAF transfer is accurate, if it isn't then all bets are off. So how your setup reacts to fuel pressure is dependent on many variables. Not knowing your combo, if it runs good with no detonation then your probably ok, to be sure a WB02 is the only way to know.
Ok, after checking your garage...your setup is pretty close to my original setup and 37# FP was ideal for that before tuning with Tweecer RT. After Tweecer RT 39# was ideal so you should be ok.