The Domane/Roubaix debate is a good one. Probably the top two premier endurance frames on the market, though I am sure others prefer a Defy or something else. The Domane and Roubaix have slightly different personalities but each are great performance bikes that are easier on the neck and back for long legged guys like me in pariicular where this type of geometry really helps. I have written before that a long legged guy will fit on a Roubaix exactly like a short legged guy of the same height will fit on a Tarmac. That is why fit is a bit misleading for many...a parallel universe of same height riders which colors the preference of many for a given frame type.
The Domane has a pretty short top tube if you check the geometry chart for its height. So the geometry is quite different than the Roubaix...which has for example has a 58.3mm top tube for a 58cm bike. The Roubaix is tall but of average length for a race bike. So I were to ride a Domane and would love to have one in my stable with new Red or say DA9000, it would be one size up from my Roubaix to get a taller head tube and longer top tube.
For me, I need the long top tube of a race bike to stretch out but a tall head tube for my long legs. Without a tall head tube, my drop is uncomfortable for long distance riding.