Ultimately Damien is correct and is making a valid, if somewhat advanced, point. Calibrating pressure for maximum flow though a series of timed, identically prepared shots is optimal.

The simpler point is that the optimal setting is basically never above ~9bar. Personally my OPV is set to 8.5 bar and depending on the pre-infusion I use it may top out at 8 bar during the actual shot.

Sub