I had a #3 zipper on a tarp door, lots of tension across it. After a couple years it failed so I replaced with #5. I think high tension uses are better with #5.
For clothing, sleeping bag,… I use #3 zipper without problem
I have gaiters with #3 zippers. They get clogged with sand and dirt, probably better to use #5. Hard to get them to zip sometimes. I wash in machine after each trip to wash away the grit which helps.
I have an REI fleece vest with #5 zipper. I use around yard. A lot of use. After years, the zipper sometimes separates in the middle after I zip it. I think it’s just at the end of it’s lifetime.