Also, do reducing valves affect the flow badly? I'm vaguely considering
fitting one at home as I'm about the 2nd house off the main feed and get
a viscious flow rate and ~10bar which makes me eternally wonder that the
plumbing isn't blown apart.

Always fit a PRV for any system with more than 6 bar pressure. Consider one
for between 3 and 6 bar, depending on how the system performs. Don't fit one
below 3 bar.

Also, if you have an unvented cylinder, you must have one to protect that
and there is usually a cold outlet that can provide a pressure balanced cold
supply.

Christian.