I would buy some Cannondale. More sizes for good fit and they ride better than Giant's. Calfee was tested on Tour-mag and frame was not good...
Remember, it's not so easy go to 6.8kg as it may look if you are building safe and race durability bike. And reasonable sized...If you not race, why 6.8kg?
My friend was little disapointed in last summer when he build new bike:
-Giant Composite frame/fork,M-size 1060/350
-Giant composite seat post/stem/bar=hight €€€
-Full 9 speed D-A
-Ksyrium SL wheels
-TIME Impact Mag ti pedals
-Michelin Pro Race tyres....
That thing weighted 7.2kg!!!! Not 6.8kg....
Pix about it. With my Lightweight wheels. They cut ~650g...so in pix it's 6.55kg. Some may think it's not light even now but it feels "funny" light...
So most weight savings will come on wheels+tyres, tubular ones. Then you should shaw brake pad liners off, they damage hight profile rims. And they are useless. On my Recod pads, they weight 8g/4 pieces. They R.I.P now.
Cannondale uses USE? That's good. SLR is best solution for light seat. I have AX-lightness Pallas but it cost 4X SLR and saves 55g...and SLR is way better to ride. In race Pallas is good but base rides, I could use somethin softer...
stem, may be bars. (I would look Syntace F99/3TTT Prima 199 set for ~300g combo)
Rear brake could be changed to Cane Creek 200SL or similar...use D-A on front! That the way for racing...you need good brakes.
Q-releases,I use Tune's, 53g pair(full ti, not alloy!). Works as you see Jan U uses them also but look how is thightening them, they are not Mavic's.
Pedals, TIME Impact Mag ti or Speedplay.
If you don't ride hard or race and live in Nederderland (no hills) you could use some stupid light parts but I wouldn't.