Excellent advice.

And as noted by someone else, you may not need any capacity other than what's provided by jersey pockets. Have you looked into whether there is a gear drop each day? Even if there is no official gear drop, if there are manned rest stops I would be surprised if the organizer would object you ditching some clothes in one of the vehicles.

Also, if you are worried about the gearing not being low enough, look into getting a larger cassette and a long cage RD. That's what I did when I went to Italy a few years ago. I think the parts, including new chain, cost something like $100.

Whatever the solution(s), I would definitely go with the lighter bike.