Ultegra - the "sensible" choice for racers and enthusiasts alike is now back, in 12-speed form. Let's take a look at the actual weights.
Shifters :: 403g (pair)
Calipers :: 282g (without cabling), 327g (with cabling)
Front Derailleur :: 111g
Rear Derailleur :: 260g
Crankset :: 720g (52/36 170mm)
Cassette :: 294g (11-30)
Chain :: 268g
Battery :: 52g
Rotors :: 108g (160mm), 88g (140mm)
So there you have it. Only 262 grams separates Ultegra from the top-of-the-line Dura Ace spec. Please note these weights do not include the Di2 wiring, hydraulic hose length (and mineral oil inside) will differ from frame to frame and can affect total weight.