I've finished my new build of my 2012 Cervelo R3 team. I haven't started on the weight reduction. Whilst the bike feels light, it comes up on the 'cheap' luggage scales at 7.41 kg. Before the build, I weighted up some parts on the kitchen scales, and copied some weights from the WW forum databases; which i calculate to be 7.23 kg.

Frame: Cervelo R3 team, 894
Fork: Cervelo R3 team, 300
Top cap: Cervelo alloy, 10
headset: spacers FSA, 64
seatpost: 3T Dorico Team, 178
handlebars: 3T Ergonova Pro 42mm, 261*
stem: 3T ARX 80mm, 120
saddle: Tioga twin tail, 201
shifters: Shimano 6600, 492*
BB: FSA press fit, 109
crank (DS): Rotor 3D+ w/ Q rings, 355
crank (NDS): Rotor 3D+, 257
pedals: Shimano 7810, 281
FD: Shimano 7800, 73
RD: Shimano 7800, 182
Brakeset: Shimano 7403, 357*
chain: Shimano 7801, 280*
cassette: Shimano 6600, 244
wheelset: Shimano 7800, 1584
wheel skewers: Shimano 7800, 120*
tyres: Conti GP4000S, 420
tubes: conti, 110
cables: jetblk, 150
Misc: bar tape, tape, sundry, 100
computer: cateye strada wireless, 46
bottle cage: elite, 42
Total calculated weight: 7,230

I wonder if the cheap luggage scales are out by 170g (2% error).

Anyways, give me your tips on where to start losing weight, on the bike. I suspect i should start with the brakeset (~150g saving), skewers (~70g saving), chain (~40g saving) and bars (~70g saving). These upgrades could yield about 330g, bringing the weight down to about 6.9kg.

I think skewers and brakes are a great place to start. I would wait until the chain needs replacing.

I am not fully up to date on Shimano 7900 backward compatibility, but 7900 shifters are pretty heavily discounted on some sites and would save over 100 grams.