Is this mixing definitions? My perspective was from procedure design determinations for individual segments.
The Class determinations are in the .52....
Note the 140 kts is max speed for the Final segment for Class C.
The 747-800 is much more likely Class D or even E depending on loading/config.
With regards to Vso, what is shown on the indicator is based on max landing weights, if this is used when light, one will go long....perhaps the 1.23 min you are referencing is in these regards...