Interesting responses to the sizing so far!
I am 180cm / 5'11 tall with an inseam of 85cm or so.
I tested the original SL7 comp yesterday in 56cm variant and it fitted very well, so I am thinking about going ahead with the VBR 168 in 56 as well.
Only modification I have in mind will be a different straight handlebar (HB011) instead of the curved standard bar.
Before my testing I erroneously had thought that the VBR would come with a larger seatpost offset than the original, but that's not the case.
EDIT// Replacing the VBR168 seatpost with the original specialized seatpost does not work - they are not compatible and differ significantly in form - thanks to @renrew.