So I built another bike - Cervelo S3 eTap
Came out at 7.1kg. Component list with weights:
g Item 1102 S3 frameset, hanger, bottle bolts, grommets and stops 391 S3 fork, uncut -30 Less: steerer removed 70 FSA for Cervelo headset, cap & bolt 2 Headset spacers 31 Deda expander bung 230 S3 seatpost, uncut -20 Less: excess post removed 19 S3 seatpost wedge 127 Selle Italia SLR Kit Carbonio 132 Sram eTap RH shifter 132 Sram eTap LH shifter 214 Sram Red eTap RD, no battery 136 Sram Red eTap FD, no battery 24 Sram Red eTap battery 25 Sram Red eTap battery 116 Red Aerolink rear brake, no pads 120 Red Aerolink front brake, no pads 31 Zipp Platinum Pro Evo pads (4) 70 FSA hybrid ceramic PF30 BB 3 FSA BB30 bearing covers 711 Rotor PowerLT 175mm with 52/36 Praxis Works rings 6 Rotor BB30 spacer (metal) 124 3T ARX II Team stem, 100mm 221 3T Aeronova Team handlebars, 42 236 Sram Red 22 chain + quicklink, sized 165 Sram XG1190 11-28 cassette 560 Vittoria G+ Corsa tubulars, 25c, x2 56 Zipp aero Ti skewers 850 Zipp 404 Firecrest tubular rear wheel 660 Zipp 404 Firecrest tubular front wheel 53 Velox 14 tubular tape 19 Nokon outer + liner, front 9 Sram brake cable, front 37 Nokon outer + liner, rear with anti-rub sleeves 15 Sram brake cable, rear 85 Elite Custom Race stealth cages (2) 208 Speedplay stainless pedals 5 Helitape (DS chainstay) 57 Fizik superlight 2mm bar tape 51 K-Edge Garmin mount XL 7053 Total
I assume the difference is rounding error (including my PT hanging scale only measuring to 10g accuracy, so the wheels and tyres are only really approximate) plus carbon paste, cable ends and other bits and bobs.