Based on what you've said, you should make the switch first. Switching your future contributions to 100% international won't budge the percentage much (100% US on 220k account). So even the low end of your range, 25%, will take some time. I would urge you to start now, and worry about 25% or 50% after you've started the switch to international. Consider that so far, you let the account reach $50k... $100k... $200k with zero international. I wouldn't put that off indefinitely to do more research when you're already convinced you need at least 25%.
Or to put it another way, you're convinced of 25% international, so use that goal. Then research if your goal should become 50%, but get started first.