I've got a couple of WarmShowers guests staying tonight - flew in from New York State a few days ago and are heading south tomorrow. Their current proposed route is over to Innerleithen and then over to the coast at Berwick upon Tweed. They had wanted to ride the coastal route, but had been told that that way lies Certain Death and that they must not do it.
I'm not sure Innerleithen then east is any more likely to avoid close passes or other driving idiocy - indeed, if they head via Haddington to Dunbar rather than though North Berwick it might be worse. She is new to cycle touring and he is hopeful this trip won't put her off forever.
Anyway - I said that I would, for preference, take the coast, but that I would also seek the sage advice / opinion of the members of respected local cycling discussion forum CCE.