Modeling Pressure Zones (EPANet)

[Auriferous]

I am using EPANet to model a moderately sized subdivision (about 300 lots of single-family). The trick is that we only have one source (a main extension that isn't built yet) coming in at about 2/3 up from the minimum elevation of the site. The total vertical difference of the site is about 120'.
This makes it difficult to maintain fire flows (1500 GPM at 20 psi min.) at both ends of the site without what seems to be a high number of PRV's. I've got it set up with 10" mains looping throughout, with some 8" connections and 6" in cul-de-sacs.

So the question is this:
What's the best way to identify how to split up the site; and if I'm going to end up with residential PRV's on, say, 40% of my lots anyway, should I be trying to keep my pressures below 60 psi, or let them go on up to 100, within the capabilities of the distribution system?

 

[RWF7437]

Generally in our part of the country (USA) pressure zones are set at about 200 ft elevation difference. This gives a minimum pressure of about 43 psi and a maximum of around 130 psi. We rarely use PRVs for any pressure under 85 or 90 psi. PRVs waste energy; that's how they work. Plumbers think otherwise but for new houses it is doubtful such pressures can cause damage if the Plumber dooes his job.