I have a Roubaix and would HIGHLY recommend it for your week long 500 mile trip. The only reason I'd pick the LHT over the Roubaix is if you needed to carry all your own stuff. But otherwise, stick with the Roubaix.

During the summer of 2010, I rode my Roubaix from Louisville, KY to Philadelphia, PA - 700 miles in 7 days. Then this past summer I rode from Seattle to San Francisco - 1,100 miles in 11 days. Both times I rode the Roubaix, and both times it was PERFECT!! Just do it and have a blast!