I would pick Ultegra over DuraAce unless you are racing. I think DA is less durable because it is designed to weigh less and that means less material and potential structural issues. Perhaps the difference is unnoticeable unless you ride it hard. $$$ does not seem to be an issue so I recommend test riding Di2. It's amazing, but pricey. I hear good things about the Roubaix, but I hate the look of the snakey seat stays and the zertz inserts are ugly. I like my Synapse which is in the same "plush" category as the Domane and Roubaix. So..... have you made a purchase yet? Personally, I might like to try a nice Lynskey with Di2 for something different.