I have read the complete thread and I must thank you for the outstanding effort to lead and report such an interesting experiment!
Grids seem actually to be the most effective planning system for SC4 cities.
I find it funny that a lot of people keep talking about cities with grids in contemporary USA: does anybody remember that grids were commonly applied to city construction by the Romans, many hundreds years b.C.? And they had been used even by Greeks (remember about the city of Miletus, in Anatolia!).
What worked for millenniums in real cities, still keeps working in sim-cities
Keep on with your great job
and thank you again