We did the last two days road book only. It's entirely doable, just makes it so you have to backtrack more when you get off course and stuff starts not making sense.
I think I was actually faster overall road book only because I stopped staring at the gps and started using the milage.
I plan on having a GPS to minimize the impact of navigation mistakes.
I think the husky went the other direction and they didn't use a roadbook at all, just navigated via gps. That seems harder than the opposite.
Thanks to Scuderia West
for their support in the 2013 Mexican 1000