I would start at around 150 as a baseline. My personal calls range from 175-225, depending on the thickness of latex. Pick a cut and build 3-5 calls at the same time with same cut, latex and stretch and see if you are onto something. If not move down or up 5 on the tension to you get to where a call kinda sorta fits you. There is so much that can go into a call. There are some latex that might be .003 in thickness, but you cannot stretch it to the same level as another color of .003 from another supplier.
I could ramble on for hours about making a mouth call, as to what is good or bad about many of them.
I had a young man come to my house last week for some mouth call help before he competed in the Grand National. I tried to make him a 2.5 reed ghost cut that was similar to one he was already using by another well-known caller. My first attempt, he sounded like he was going to bust the windows in my house it was so high pitched. The next call was less, and it was still high pitched. This went on till I was all the way down to 85, and his calling was still high pitched.
So the calls he had were stretched to Less than 85. My point to this rambling is when you buy a call, you are buying that call makers one size fit all stretch that goes with that cut. So if I had made a call and mailed to this young man at my standard stretch, he would have said my calls are Trash.