Calculator shows for 5gpm flow, 170', plastic pipe:
1/2" id pipe: 41psi pressure drop (1/2" actual size, not nominal)
3/4" id pipe: 5.8psi drop
1" id pipe: 1.4psi drop
So that means if you have a normal 40-60 well pressure switch, with 1/2" pipe you'll have basically no flow at the bottom side of the pressure cycle. Not sure why you want to use pex instead of polyethylene tubing, it's cheaper and used all the time. I'd use the 200psi instead of 100psi rated stuff, it's a little thicker wall and stands up better to rocks and abuse. The fittings for poly are cheaper than pex too. I went with 1" poly out to my barn.
1/2" id pipe: 41psi pressure drop (1/2" actual size, not nominal)
3/4" id pipe: 5.8psi drop
1" id pipe: 1.4psi drop
So that means if you have a normal 40-60 well pressure switch, with 1/2" pipe you'll have basically no flow at the bottom side of the pressure cycle. Not sure why you want to use pex instead of polyethylene tubing, it's cheaper and used all the time. I'd use the 200psi instead of 100psi rated stuff, it's a little thicker wall and stands up better to rocks and abuse. The fittings for poly are cheaper than pex too. I went with 1" poly out to my barn.