Vietnam 10days incl motorbike tour

I have been to Vietnam twice, once to the south in/around Saigon & the Mekong, and once to the north in/around Hanoi & Sapa.

I am going back with my Dad for a 10 day trip, and am keen on doing a motorbike tour (say 3-4 days) around the northern hilltribes area.
I have hired a bike around Sapa before for day trips, but no full-on motorbike tour yet.

Any recommendations/Advice?

Is it better to base 10 days all around Hanoi/Halong/Sapa area or would it be worth trying to squeeze a trip on the Mekong by flying domestically down to Saigon for 2 days on the Mekong before flying home from Saigon? (or is that just too much)