@Gibbo - took us 5.30hrs in total with about an hour at feed stops. Most people I saw were enjoying the day and not in a rush.
That's a sensible approach. My question was prompted by (A) seeing some riders in D Mains mid-morning and, (B) later seeing some participants - including kids - looking relatively fresh near Blackhall.
(I'd be a big sweaty mess - even at 10mph - by the time I got to Edinburgh... if I made it at all.)