I personally think steel is the way to go. BUT, last summer I did a long tour on a super light high end CF climber (04 Trek 5900 Superlight). I swapped out the wheels for 650B so I could get some comfortable 32 Grand Bois tires. With Chris King hubs those wheels were actually lighter than the race wheels that came with the bike. Seat bag and handlebar bag and a small frame bag. Loved it. I have other experiments planned but I still think lightweight steel is the way to go "light" on a tour.