B767-200 17.9:1 AFM had it.
B727 - supposedly 17:1 (I'm guessing it was just an estimate).
B757-200W and 737-800W - approx. 19.5:1 calculated sink rate/TAS in the airplane.
B777-200 - guessing close to 19:1. It seems to be similar, but slightly less, than the 757W and 737W performance
B787-8 - 21-22:1 per Aviation Week and Space Technology
18:1 is simple math - FL(minus one zero) x 3 = glide distance. Eg FL300 - 30 x 3 = 90.
30,000' = 5 nm. 5 x 18 = 90.
10,000'/250 kts/no wind - 35 nm away should make the runway. 40 nm is tougher and wouldn't be worth the risk in real life(IMO)(simulator profiles).