I can't think of a tougher 400k than one that involved no hills whatsoever. That would not only be mindnumbingly dull, but would involve no chances whatsoever to get out of the saddle and give parts not yet fully evolved to carry the weight of a human being the odd rest from that task.
This ride sounds perfect in the hills-to-break-up-the-flat stakes.
Ask me again for my opinion of hills at the end of the Wu'ze next weekend.