The pump should really be a 7M but a 6M may not make much/any difference on DHW.
I would now look your problem from a different angle, you basically want to know if the boiler is giving its full rated output and this is the easiest way to do it IMO. If it is, then you can look at flowrates/temperatures later.
I would, first test, turn the DHW temperature control to Max then switch to Eco mode, this will have no tank heating and the boiler will act in normal combi mode, then open every hot tap fully, then take a snapshot of your gas meter and exactly 3 minutes later take another and post back your readings.
Your boiler is 29kw (maybe 30kw) so at full ouput I would expect to see a 3 minute gas consumption of 0.155M3.