Your avatar shows a a classic touring/comfort set-up. Good. I go for maximum comfort every time. My Sequoia Elite weights 30lbs with a Brooks 17, a medium bar bag, and two large water bottles on it, but is extremely comfortable on centuries because it's setup like your Saluki, even tho they are totally different approaches to road bikes. Plus, the jockey weights another 235.

I agree that you should be hitting 80 miles with no problems before you go for The Big One. You'll find all the little things that matter at about that distance, and will be able to address them. For instance, at 235, I need to eat alot more after 50 miles to keep the furnace hot. The last 20 miles of a century are largely mental. If you are dialed-in for 80, it's a slam dunk, if you leave the kitchen sink in the kitchen