Splitting days between HCMC and Da Nang

This is the secondary leg of my Asia trip (from the US) mid-January. I have 7 nights how would you suggest it be split up? Thinking 3 in Da Nang with a day trip to Hoi An. Then 4 in HCMC before returning? I am totally open to other cities (Hanoi?) as well except for the return flight from HCMC is fixed. Not into clubbing but do like an active local bar / pub scene, restaurants, some sightseeing.