Assuming they have the same crankset - the 16 pound bike with a 28 is probably going to be easier than the 19 pound bike with a 30. If it were a 32 I think it would be more noticeable. Or if the Domane has a 53/39 and the Madone has a 50/34 then the answer is more clear.

PS I think 100 miles at 4500'ish feet climbing isn't really that hilly.