B767 Gear Down Dispatch
 

Hello,
Seasons Greetings to all!

A quick question (for those of you not watching the cricket) regarding gear down dispatch in the B767:

Why are climb / turbulence pen / holding / descent speeds based on Vref 30 + 70?

It seems strange to me based on the "man. margins to stick shaker" showing that being clean gives a much lower avail margin to stick shaker than Flaps 1 or 5 so I would have thought Vref 30 + 80 would be a more appropriate min speed for gear down dispatch.

Thanks in advance.