In my opinion, zones 4+5 should be between 40-60%.
Zone 5 should ideally cover all borders, waterways and roads. This helps link zone 5 areas together, with all you permaculture neighbours (along borders) and interconnects the parts for wild life (waterways and roads).
When doing the design, I think it is easy to plan zone 0, 1 and then 5. So that you have a rough idea of where it goes. You can modify it later if the areas aren't working perfectly for you.