I built a frame from True Temper RC2 tubing (think Reynolds 531) in a 57cm size. The frame was 4.5lbs on the nose. The fork was 1.5lbs on the nose. Using robust Suntour components with indestructible Araya DP18 rims and 36 spokes, 28mm tires, the bike came in at 25lbs with rack and H2O cages. Friction shift and freewheel with Suntour Barcons. 6lbs frameset can easily be turned into a 21lbs complete bike.
At the same time my buddy Dave built his from HOX in a 59cm size and the frame was 6oz lighter than mine! Wall thickness was the difference.