I'm far from being a class 66 fan, they are far too late for my chosen time period and I get bored of seeing them at work... But I ordered a Colas one when they were announced, then yesterday when I saw 66789 in large logo blue had been added I had to order that too! I still don't like 66's but I couldn't resist these!
I'd vote for the Royal Scotsman pair too.
As for sound, I've just gone for DCC ones, but if the Scotsman pair (or just one of them) were done I'd want sound, but if the sound files were supplied by Olivias I would definitely pass and just get the standard version and add superior sound by biffo or someone else later.