Sam,
If mileage is the goal, then there will be little difference between PVA & MVA. MVA will give a smoother idle, more vacuum, run cooler at idle & have better tip-in response [ this is based on comparing idle timing after adding MVA...with the stock ign timing ].
And I can tell you from years of experience, your engine will want AT LEAST 30* [ probably more ] for best idle. MVA is one way of providing that. Beware of the bullshit in another post.
View attachment 1716282368