You will be happy with the Roubaix it will be well suited for your objective. I have the Dura Ace Di2 S Works version and very happy with the bike. If you ride includes some challenging climbs you can easily put an 11-32 Ultegra cassette on the bike with no modifications. If you want the S Works version it's your money and want to buy the premium version go for it. As far as the ride goes I am sure you realize it will be very difficult but anything worthwhile usually it is.
"We choose to go to the Moon...We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard; because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one we intend to win, and the others, too."