UCI expected to approve Road Disc Brakes for 2016

[g-boaf]

But the bike weight is only a small part (~10%) of the total weight. If you are at your lightest weight you can be, then reducing bike weight is the only way. Otherwise reducing rider weight would be more advantageous.

In my experience I have been down to 56kg weight (from 59-60kg) but that takes an enormous amount of riding to do - that's doing consistent 800-1000km weeks because I have no interest in radically changing my diet. At that level I basically eat heaps. You need it to keep going when you ride that much.

I was riding a 7.2kg bike at those times. The really light frames weren't as common back then. I would have liked to have had my Canyon back then - I was very fast at that time. It was still 4 years away from being released.

[Anrai]

Based on your number above of 4.5W/kg, that extra 100g requires an extra 0.45W to push around

By my understanding it's not completely straightforward like that; increasing upward gradient would exponentially increase the wattage requirement above what you'd need to push the weight on the flat, as you're acting against the additional force of gravity.
I don't have answers for whether it's worth spending hundreds/thousands to trim half a kilo, though.