I admit to being astonished that FlyingOfficerKite feels a B737-300 would glide only 1nm per 1000ft. That is worse than a Hunter with its gear down. If these numbers came from a sim then I would suggest the sim was in a suspect state of health.
In my book all modern airliners (when clean) are very efficient cruise machines which means they have to be good gliders. Weight of course has no effect on any gliders descent angle – only its best gliding speed which will increase with weight. Which is why during competitions if gliders need to go a long way into wind they load them up with water ballast to help them penetrate (at no detriment to their gliding angle).