I've been wondering and searching for a while and since i've not come to a conclusion, here is my question:
I've got a custom cannondale bad boy weighing 6.8 kgrs. As you can understand i am a weight weenie guy. My drivetrain has:
1. Clavicula mtb dp (2X10), 44/32.
2. Sram red xg 1090 10 speed cassette (26-11)
3. Dura ace 7900 front-rear derailleur.
4. Shimano sl r770 10 speed shifters.
Everything is working perfect except the fact that the sl r 770 shifters are very heavy (about 260 grams).
I know that the 10 speed xtr m 980 shifters weigh about 205 grams and i've heard from some people that they should work fine with my drinetrain. Is this true, are they compatible with my dura ace front and rear derailleur?
And if there is a problem with my rear derailleur what's the weight difference between da 7900 and xtr 980 gs rear derailleur in order to make it work?
Thanks in advance for your answers.

You can't use the XTR shifters with the dura ace rear derailleur. I don't know the weight difference between the two derailleurs, but it should be about 25g if you skip the "plus" variant.
the front shifter/derailleur will be fine. You lose the trim function.

From what i've read the weight difference between dura ace 7900 and xtr 980 is less than 10 grams (173 grams xtr m980 gs and 166 grams-dura ace 7900.
Together with replacing sl r770 shifters with xtr 980 shifters there would be a weight loss of about 50- 60 grams. Of course one thing i could do is remove the shifter indicators from sl r770 shifters and lose without any cost about 30 grams.