As @Rachel says, we’ve seen some good results from people running their sensibly-sized pumps smoothly.
Mine is probably the most oversized one we’ve got on the forum and that leads me to:
So I have the luxury of mine always being able to deliver whatever heat I ask of it, but it only runs smoothly when it’s about -3 °C which is pretty rare in the UK. I simply replaced my oil boiler with an ASHP with the same output.
Here is 2022-01-15 and it wasn’t very impressive at all - that’s a lot of kWh:
For comparison here it is when it’s warmer outside and it modulated down, but the house was getting too warm with 6kW input. Similar situation even with 4.67kW delivered.
So if I were looking at a “too big” heat pump I’d want one that could modulate down much further (in the case of my house, to about 2kW delivered) so I could run it more smoothly.
Having said all that, I feel @Jimbo1 is saying something that I feel too. Having the heat pump on all the time may be unnecessary and leads to you spending money running it overnight when you could potentially let the house just cool down gently if you have enough thermal mass. The occupants are in bed, under duvets, and the house doesn’t need to be kept warm for it’s own benefit. In one of my friend’s passivhaus new-builds they purposefully added a core of a large mass of concrete to stop the temperature oscillating too wildly. I haven’t looked into the research enough to have an informed opinion though.