Check oldpunk's sticky in the Equipment forum about building a regulator. It has the answers to everything you need to know.
As to the pressure, the first reg you linked was a 40-175-320.
40 = Series 40 model
175 = Max output pressure in PSI
320 = CGA320 nipple and nut
Additionally, if you click on "larger image", you can see that the red inside numbers are in PSI. The highest number is 200. Even if you didn't know that this model was rated for 175psi, included gauges are always a bit higher than the maximum output pressure.
And I *still* would recommend an Evilbay used single dual stage over a new single stage due to cost.