One last question and then I swear I'll leave you alone. When you break in a gi with the vinegar on hand; do you wash it in warm or hot water as part of that break in process. Will water temp alter the way the gi comes out in the end with the vinegar added to the mix?
I have one gi that has shrunk a lot with warm water and hot laundry dry. Now I only wash it in cold water and hang dry. I just ordered a new gi and I'm a little hesitant to "break it in" for fear of shrinkage.
You're right to be cautious - both higher water temperatures and agitation will shrink a gi (so will drying with heat). Vinegar doesn't shrink clothing at all.
The hotter the water, the more the gi will shrink - especially if you run it on the agitation cycle multiple times.
With cold water, the agitation doesn't shrink the gi to nearly the same extent - though it still may a little bit. I've personally never found this to be a problem since a half inch shrinkage in a gi is not usually an issue for me.
So - for a gi that is slightly too large, I'll wash it cold and break it in with the repeated agitation and vinegar. For a gi that is much too large, I'll wash on the hottest cycle and add a pot of almost boiling water to the load as well. I let it agitate several cycles. Then I rinse on hot and throw it in a hot dryer. Sometimes, I need to do this twice or three times to get the shrinkage I need.
If you have a gi that fits you perfectly - then I would baby it. I would probably only break it in with an overnight cold vinegar soak - no extra agitation. Run it in a normal cycle on cold, rinse in cold, and line dry. It may not be a soft as you'd like but better to start off a little too stiff then a little too small. It'll always get softer on the mat.