Re: SD and HD sync issues
Thank you both. I've tried turning off just about everything, and the only setting which has made a difference at all is the IFC - intelligent frame creation.
I've been trying to eliminate the source components from the equation, so tried using the built-in iPlayer app - which definitely has minor sync issues. Then I reverted to watching live tv via V+, and that didn't seem to bad.
It's unfortunate that I don't have a freeview aerial so I can just use the inbuilt tuner and the BBC's test card to show for once and for all that the TV has a problem.