I am using the Google Spreadsheet API to update a spreadsheet with a lot of data (hundreds of rows and around twenty columns).
I have tested making a batch call to u
If you are updating entire lines, you can try working with list-based feeds:
http://code.google.com/intl/fr-FR/apis/spreadsheets/data/3.0/developers_guide.html#UpdatingListRows
It will allow you to update values (not formulas).
If you still have performance problems, you should switch to something like a relational database server or google's datastore (if you are working with google app engine)