Hi des – I am Mr wind deflectors – they are useful to clear steamed up windows quickly with windows cracked open – maybe first mile at the most – I have auto regen on all the time and rarely use a/c – I live just outside the M25 so traffic is mostly busy – I don’t drive slowly – just go with the flow of the traffic – so no point in hard acceleration or braking.
We haven’t had a frost yet so temperature could be a factor. There was an occasion where I had fan on and wasn’t aware of it – I always have music on from phone. But it did lower the miles.
So I would definitely have auto regen on and let it do the braking down to under 10mph and don’t accelerate hard when a gradual catch up to traffic flow works.
If I’m cold a/c goes on and I max speed limits where I can.
Good luck with your trip – hopefully it will give you a better understanding – tho I would be doing 65 on motorways – it seems to be the sweet spot ?