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Not exactly a weight weenie bike (weighing in at about 8 kilos) but I have used non expensive and non fragile parts.
This is my training bike (I race track mostly) and could be easily lightened much further with carbon wheels, bar and stem etc and upgrades to groupset and switching back to non powermeter chainset.

A basic build list
Dolan ares frame and forks (size 56-basically dolans large)
Quarq sram s900 chainset
sram gxp bottom bracket
shimano ultegra shifters, rear and front mech (front mech is triple version fro previuos 10 speed ultegra incarnation)
FSA slk brake calipers
mavic askium wheels
hutchinson fusion tyres
FSA wing compact bars (44cm)
fsa os 115 stem (10cm)
3T dorico team carbon seatpost
fizik antares saddle
garmin 705
bontrager rxl bottle cages
bontrager bar tape
jagwire cables

comments welcome and I am fully aware that I have broken the weight weenies cardinal sin of photoing a bike in little chainring etc but I literally just finished building it and wanted to get the pic