Sorry I’ve not got back with the buffer heat temps, it’s getting towards the top of my list of priorities in the list time I have. Being out of the house for 14 hours a day doesn’t leave much room for other stuff currently.
Thanks @Ian_Calderbank as well for the expansion on the flow rate.
@Zarch Most informative post. I have seen heat output hit 6kW on DHW runs, but I think that 28mm all the way to the DHW cylinder. So flow rate isn’t a limiting factor on the ASHP side of the buffer then at least.
Yes “everyone” is always on about what valiant curve they’re on so at least now I can match them with ease. 
With the recent colder weather I think it’s not doing to badly, this was at -2˚C outside, house was heated to 21.2˚C.
Thanks.