We have a few area's with 175 psi .. It's pretty insane
From experience and if you follow a flow chart 17 GPM on a 3/4 line with 175 psi is actually pretty low gpm. If you had the 3/4 copper line cut fully it would probably be 30 gpm+. Depending on several factors
However the higher the psi the more pressure loss happens and water hammer. Ontop of the galvi corrosion /hose bib is probably how you got your gpm.
I Highly Highly Highly Highly recommend to install a a pressure reducing valve AT your water meter ( Just after) You can request your water district to install one prior- they may or may not do this though.. The reason I recommend this is because of possible future leaks in your service line leading to your house. I deal with leak detection on service lines a lot and the pressure plays a huge role in the leak. I've seen many leaks just stop with reduced pressure... This pipe is your responsibility not the cities.
To code an irrigation system is rated for 5 FPS (Feet per second)
If you follow this flow chart
This is just an example.
But lets say you want 70 PSI leading up to the irrigation system and to the PRV at the house.
To set the PRV correctly at the meter Calculate your length from the meter to your house and the elevation difference .
For example if your house is 100' from your meter with a 20' elevation gain. Pressure loss from the elevation gain is .45 ( rounded up from .433) per foot. so 20x .45 = 9PSI . Factor in to reach the goal of 12 GPM on a 1" copper line ( 5 FPS) of 100' your water pressure loss is an aditional 5 fps. Altogether rounding up to a total of 15 psi
So to reach 70 psi at your house in this situation you must set the PRV at the meter to 85 PSI. It may be confusing but I recommend to do this.