Andrewwynn is again spouting a bunch of BS. The fuel pressure regulator line is vented to the intake boot on the E53 M54, not attached to manifold vacuum. At most it might compensate for a plugged air filter. If you had it attached to manifold vacuum it would drop your fuel pressure proportional to engine vacuum and cause your engine to run lean with the fuel trim trying to compensate
54-55 PSI engine/pump running sounds right to me but it's been a while so I might check again if I get a chance. It's pretty hard to get too much fuel pressure unless you put pressure on the regulator diaphragm.