Water Injection/N2O & 91 Octane

For illustrative purposes let's take a mild 91 octane pump gas 468 cid BBF 9-9.7:1 CR mild hydraulic cammed 520-580 hp. Let's add a NOS Cheater 150-250 HP plate. Would a direct port Water Injection allow a 91 octane tune for engine & N2O?

With a 9.7 static comp there is no need for water inj with a small shot like a 150-200 as it is already cooling things off.

Water and meth inj is a good thing and works well in a n/a combo also but the nitrous is already doing its job for it.

This is jmo. Now take that motor slap a f3 charger on it and meth inj  it will be better as it cools the iat.  nitrous doubles with boost so you could do away with meth and spary it a 50shot and its like spraying 100. While still dropping the iat's to a safe level. Just keep in mind you are still on pump gas and on edge.

Generally speaking how much N2O and or CR to I need before I need water injection for pump gas?