Please provide some more detail re the frame and groupset selection.
I'm currently riding a Kona Honky Inc which is heavy, but works, and am working towards a Di2 equipped carbon framed bike as the next step (may even be Ti), but must be a road bike, not CX.
I use the RT-86 Shimano IceTec rotors and whilst not the lightest, they are very good and are comparitive in weight to the G2 Cleansweep rotors for the same size.
I use a 180/160 combo, as Im a bit bigger, but a 160/140 combo would suit most people (as long as sensible discs are used).
140mm discs on road bikes seem to be gaining momentum. And there has probably been a lot of talk in the bike industry of which size discs would become the norm on road bikes. I, myself, was thinking of doing 160/160, but am open to other possibilities. Certainly smaller rotors look better, but bigger rotors have a mechanical advantage.
Colnago's carbon bike with discs uses 140 rotors front and back if I am not mistaken. And 140mm does seem to be gaining some traction from other manufacturers too.
Kona's road bike that is coming out soon, the 2013 Kona Rove, has 140mm discs front and rear.http://cog.konaworld.com/archives/12172