We're on a combi-boiler (WB28SIii), have good cold water pressure, and
at the moment, c/o the kitchen sink, it chucks out 9 litres of hot
water per minute - although I believe from a previous thread you can't
equate throughput with pressure.
I've tried to play safe when ordering taps for the bath / sink by
going for 0.2bar jobbies

FWIW our current bath taps are these - screwfix ref 10532 - says
suitable for high or low pressure systems, but doesn't specify flow /
pressure rates.

The shower off it is certainly better than some electric showers i've
been in (where you can pi$$ faster than the shower dunks water over
you) - but would I be right in thinking that the shower head adds
quite a lot of restriction to the flow, so something like screwfix ref
89618 might be more of a sad dribble than an actual shower ?