Are you on a pump system? If that's a PRV, what's it actually set at? Showerheads are limited by federal regulation to a max of 2.5 gallons/minute. You can sometimes take out a restrictor in the showerhead to get more flow, but it won't make any differece to your incoming pressure. Just like when you put your finger over the end of the hose, it can give the appearance of higher pressure. Some showerheads are better than others, but first, what's your incoming pressure?