Ed Sirett wrote:

If your incoming main is truly 10bar then a PRV is called for. Almost
everything will be having a hard time (including the boiler which may well
be rated for as little as 8 bar max). Taps will jam and spit and wear out
quickly, cisterns will be whistling as they fill, they will probably need
new washers frequently.
If you truly have 10 bar then I don't think you'll need to worry too much
about the resistance put up by the valve.

It's certainly well over 7bar - the gauge I had only went up that far -
but there was still plenty of scope for going higher (I'd only cracked
the tap open slightly to let it rise slowly.) I replaced the main toilet
cistern with a Fluidmaster valve as it did whistle awfully and it was
lovely and quiet afterwards. Trouble was it filled the cistern in 12sec
flat and, finding the overflow couldn't cope (surprise), I turned down
the ball valve which made a whole new range of noises. A bit of
tweaking made it play an acceptable note but it's not ideal.

The boiler is for a different property but again there's good pressure
and flow so unless there's a good reason otherwise I'll shove one on
there too.

Scott