I think the glide performance of airliners has been getting better. The 777 which I fly now is noticeably more slippery than the 737 I used to. A 777 will accelerate on a 3deg slope under most conditions, meaning the glide angle is > 20:1. OK, the engines are still running at idle but this is only going part-way to counteracting the drag of the nacelle and the windmilling front fan. If you took the engines off completely, I wouldn't be surprised to see 25:1 or better, although it would be flying a little fast to thermal efficiently.
I also fly a self-launching sailplane. It has the fuselage of the ETA but slightly less span (28m vs. 31m), a sort of ETA-lite. They don't quote any performance figures (adequate, sir!) but it seems to have
very long legs...
