If you are going to use a smaller 210 gyuto then you should look at a taller one for making onions fall apart
I work in a compressed box area I think a 240 wouldn't be a problem so I ordered one this week.
A little extra blade length will make the prep work less of a chore. I have to play devils advocate and suggest a longer blade. But if you insist on a 210 check the heights. A taller blade is gonna be an important feature.