I believe the main drain stack needs to be 3" minimum, would it be wise to use 4" instead?

Biggest issue I have found with 4" is that I cannot fit it in a 2x6 wall. This will be a new house construction, so if I need to I can build a bigger wall, but if my gain is minimal, I would bother with the hassel.

Just looking for thoughts on the best way to go. Let me know if there are other details that will help with this, below is what I could think of.

-2 Full bathrooms on 2nd floor, share same wet wall
- Laundry, 1/2bath and kitchen on main floor right below the 2nd floor bathrooms
- Basement unfinished, but will be stubed for full bath

Thanks!