Surge - is the question directed to me? I don't know. Went to the training center and asked the question. The guy dragged out the official Boeing book(I don't know which one) that the company uses to decide what information the pilots do, or don't, get in our AFM(reduced from Boeing manual).
Based on inflight experience, TAS, sink rate, etc, etc. I'd guess the 757 and 737-800 wingletted models get about 19.5, or better, L/D.
mathy stated that the 777 gets 19.26:1.
Attempted dual engine flameout landing from a fixed spot(10,000', 250KTS, 35 n.m.) in the 737-800 W/L, 757-200 W/L, and the 777-200. All appear to have almost the same glide performance as all three a/c made barely made the runway.
Based on the performance observed, and mathy's comment, 19.x seems reasonable.