The string alloy can greatly effect the output of a pickup. The inner core of most acoustic and electric guitar strings is made from various gauges of spring steel or piano wire. The spring steel can be wrapped with various material shapes that add diameter and tension to the string. Strings can be flat wound, round wound, semi-flat wound, ground round, tape wound etc. The pitch of a string is how closely each turn is next t each other. The tension of a string can vary from string manufacturer depending on their manufacturing procedures and especially materials from suppliers. There are many string designs and combinations of materials that can determine the output and tension of a string. Some wrapped strings use a thin core spring steel and heavy outer wrapping and others use a heavier core spring steel and thinner outer wrapping.

I would contact the various string companies and ask about their models and specifications. Some will gladly give you the information and looking through the internet can give you all kinds of advice and information. I hope someday soon you will find information available about strings as you are beginning to find about pickups.