You need enough pressure at the injector to completely fill the lower chamber. If you have that sufficient pressure, more is not going to do anything. You cannot compress a liquid (at least not enough to make a difference), so once the injector is full, that's it.

Ford engineers have apparently figured that at least 45 PSI at the fuel bowl, with the stock banjo bolts, will supply enough pressure at the injectors to do the job. I don't believe that any additional pressure is going to make a difference.

If you have less than the specified 45 PSI, you may not fill the injector and it may be damaged. Since the specified range is 45-75 PSI, it seems logical that hitting that number in the middle to upper is prudent.

Actually, if you stop and think about it, if there is a restriction in the banjo bolt and you remove it, it may actually be possible to get too much pressure at the injector and push fuel past the o-rings.