Hard to say, what part you should ride. If split entire route on two, both parts are different. Depends if you ride loaded or just with water and cliff bars. I second that southern most 30 miles are very quick ride. Northern half less ridden but offer absolutely different landscape and experience.
For true off-road and physical challenge ride Northern part. For fast miles go Southern part. But better to do the whole thing, of course.
And don't forget to check water level in Little Missouri before starting your trip. Current is fairly strong even when knee-deep. Otherwise you'll have to put extra miles to cross it over bridge.
Good luck on your trip and post pics with report for us to read
