I haven't taken my Swift on a long ride yet--it's my commuting bike--but I did my first 200K, 300K, and 400K brevets recently on my road bike.

+1 to food being key. I don't think it's possible to predict what you're going to need at mile 200 based on how you did on an 80-mile jaunt, so you might want to throw a few gels and powders in your bag just for emergencies, and maybe some electrolyte capsules.

I also think bike fit is just as important on a really long ride. Things that don't matter much in the first 50 miles can really hurt you in the second or third 50. I haven't ridden in three weeks because of the ITB problems I developed on my 400K, so this lesson is fresh in my mind.

(BTW, I have the Nelson too. Nice bag!)