Numbers Jock.
For B744ER with GE CF6-80C2B1F engines close to standard conditions close to sea level.
Using Full rating thrust, Vs1g @ F20 varies from 160kt @ 412T to 120kt @ 230T whilst Vmca is 120kt and Vmcg is 126kt.
Before you say "gotcha" at the 230T mark, nobody would be at FR at this weight, rather Rtg 1 with Vmca of 117kt or even Rtg 2 with a commensurate reduction in Vmca.
I reiterate, I have no idea how this could be demonstrated but since it is certified data that's what we use.
There's a bit more to tail fin sizing than 1EO ops on the ground but that's a whole new thread drift from the one we are currently involved in.