I had occasion to walk around Montrose Terrace and Regent Road yesterday afternoon.
Traffic is hellish, huge tailbacks leading to 'frustrated' drivers jumping the lights at the junction with Easter Road, thus blocking it for pedestrians and traffic going the other way after the pedestrian phase.
On the positive side, Royal Terrace is blocked off with barriers at the junction with Regent Road, presumably to stop folk trying to rat run between there and Elm Row/ Leith Walk. So that and Regent Terrace are very nice quiet routes for pedestrians and potentially cyclists - though watch the cobbles. Over the next year I may walk that way to the city centre in preference to either London Road or Regent Road, especially at busy times.