You might want to take a look at the following WW thread, about my steel project bike made by Chas Roberts in Croydon, England:http://weightweenies.starbike.com/forum/viewtopic.php?f=3&t=101178
The show spec is 4690g, but I would swap a few things out (like the track tubbies) for heavier-duty parts when I ride it, taking it to just under 5kg in total (On the road).
If you did without the couplings and you were a very lightweight rider, you might knock 200g off the frameset weight, and I reckon you could lose another 200g or so off the component spec. The extra weight loss would cost an inordinate amount of money, and I've run out of budget completely for the time being, so it won't be me setting any newer records!
Chas is a master builder - been in the business with his father for 50 years, on his own for almost 40. Builds very simple, very beautiful, comfortable and functional custom steel bicycles (of every stripe); took some doing to get him to build this one for me (but then I already had several of his frames by then!).
The beauty of steel is that, once you find the right frame spec, the frameset is for life - it can be fixed, resprayed, rebuilt...