There is no bike (without an engine) that you will be turned away from the start on. It's your choice, and James on the website is simply giving you some info about surfaces that might influence those choices.
I'm coming from the other direction than chris at the moment; I have the perfect bike for this except it has 2.2 Ikons on it. Whilst I can almost certainly get round a ridiculously hilly 400 in 26 hours on it as it stands, I'm looking forward to the hundreds of hours agonising over whether to go narrower / lighter / slicker tyred for the majority tarmac that this route will undoubtedly be. Then probably turn up on my nearly bald Ikons anyway and get some more sewing practice (a la Gravel Dash eh chris?