I'm travelling in UK with three cards - a Chip-and-Sign HKD MC credit, a magstripe HKD AE and a Chip-and-PIN AUD Visa Debit
Acceptance of credit cards is very good - even small merchants in UK accepted my MC. There's a £5 minimum at some places.
And UK merchants love the chip and sign MC much more - they seem to have difficulty handling magstripe cards (e.g. O2 shops don't even have a magstripe terminal)
Some are surprised the terminal told them to make me sign, and checked signatures quite carefully (tho none refused to accept)
No DCC (HKD charging) so far
I haven't encountered a Chip-and-PIN-only terminal this far (I did in Aus - Sydney Cityrail ticket purchase at night). I don't have a Paywave on me but I have my AUD chip and PIN card in case we encounter similar terminals on the UK.