For best glide, you want to go to L/D max. Usually L/D max is somewhere around 3.8 AOA I think, but it depends on the airfoil. Since civil airliners are rarely fitted with AOA indicators or vector bars, you can't really determin AOA easily and accurately. In absence that AOA readout, Vref+80 (low GW) or Vref+100 (high GS or high altitude) is a decent rule of thumb.
757 Optimum Glide Speeds
GW Vref Op Glide
160 117 203
200 133 226
240 148 246
767 Optimum Glide Speed
GW Vref Op Glide
220 119 203
300 141 236
360 159 257
Commercial flight manuals are notoriously sparse of detailed data and charts. Maybe someone else has a better ROT. Sorry, that's the best I can do for you with the data I have.