My experience is all over the place. It all depends on how "pre-shrunk" the gi is. Some can be shrunk a lot, some a bit, and some almost not at all. Bleached white gi's seem to be pre-shrunk more often. Maybe the bleaching process requires more hot water or something. Natural color gi's, maybe yes, maybe no.
Try it and find out. Don't use boiling water. You're not trying to cook the fabric (yes, you can cook any natural fibers - and this is typically a "bad thing" if you intend to wear them).
You might also try different brands. Just because the company says size "5" on the label doesn't mean it won't be too long (or too short). Find a company that you like and then find a size that's right in their lineup, knowing that it varies from manufacturer to manufacturer.
Peace favor your sword,
Kirk