Frame geometry and proper adjustment for the rider are big factors and there is often a trade-off between optimum geometry for climbing and a bike that is comfortable and stable on steep downgrades. Bikes like the Trek Domane and the Specialized Roubaix have what I would want in a road bike that is great overall. The Giant TCR Advanced Pro 2 is another bike suited for climbing and a good value at $2500 and weighs less than 8 kg. The Trek and Specialized bikes have a wide variety of components so one can get the frame and put less money in the non-essentials to get a more reasonable price of around $3500 for the carbon frame models.