Regarding the 'why', not sure, but if it were me I'd go with the lower range if I could find one. My understanding is that the higher pressure cap is to increase the boiling point of the coolant in the F/W side of the system.
Since your engine
is designed to operate at 195F max, 17 degrees below the boiling poiint of plain water
, the lower pressure in the system would help guard against fresh and salt water
mixing due to less-than-perfect sealing between the two 'sides'...