I'll weigh in on this debate with some real-life experience... We had an Intergas Xclusive 36 installed a couple of months ago. Temp for CH is set to 70 and DHW is set to 55 - I don't recall what the max temp's are in the installer settings, I assume factory default, i.e. I could manually set both CH and DHW higher than they are now. There is no WeatherComp.
I have noticed a number of times the hot water at a tap will be very very hot, with the mentioned initial slug, especially when the CH is running. We have one tap in particular, which is on a sink in our kitchen, probably only 1m from the boiler, which delivers raging hot water initially. You also notice it when using a thermostatic shower - if you turn the water off mid-shower, when you start it again you get a slug of hotter water, before the shower 'stat and/or boiler bring it back to target temp.
I'm intrigued to know if "properly setup" means more than just setting the CH & DHW max flow temp's, i.e. there is more involved in commissioning such a boiler?