Any tips for my spouse, heading off for a 600K in a few weeks?

[salsabike]

Maillotpois and some others on here, I am wondering if you have any special tips for my cool spouse. He has done a fleche and recently a 400K. In a few weeks, he's doing his first 600K. If there are any thoughts you have on how a 600K was different from a 400, I would love to hear them (you know, like having three kids is totally different---my friends say---from two, etc.).

Gah. Advice welcomed.