If they are your PRIMARY interest, bigger is better. Go 127 if that is all you are willing to do.
Remember this: The scope you see the most in is the scope you use the most.
Be honest with yourself. Most people get a grab and go for that very reason. Even tho it is smaller than perhaps they can afford. They know that they'll see smudges for DSOs and be happy to see/detect them as well as hone their observing skills in the small scope. Some get a simple but larger Dobsonian for the nights they are willing to get away. And push to is a cheap(er) option on a dob.
OTOH Burston CA seems to already be off the beaten path. Seems to be Bortle class 4 because of Sacramento. But near the edge of class 3.
Depending on budget and interests...
Goto? Go with the largest aperture you can afford AND will take out (if not permanent).
Push to? Go even larger! But make sure you'll not dread taking it out!
The 5 inch will go deeper than the 4 inch (except MAYBE on contrast / planets). But it has a narrow FOV. All scopes are compromise which is why many of us own so many.