Re Original Question
Gents (and any Ladies hiding out there)
Re Vtoss and Vy, Geoffers has it spot on.
Re the original question (why droop NR during OEI flyaway?), Crab is spot on. The aim of the published Cat-A flyaway procedure is to achieve Vtoss as quickly as possible, so that a safe climb gradient can be achieved. Drooping NR to (or at least towards) the RFM limit will provide the most efficient acceleration to Vtoss without inducing a significant ROD.
Re the debate about rotor efficiency at reduced NR, I defer to Shawn Coyle!