Up to 800MW...that's a pretty good number. Recently completed "large" farms in Europe/Scandinavia are in the 600-700MW range. But that number keeps climbing as the turbines get larger and the operators continually seek greater economies of scale.
As a point of comparison, the only existing US offshore wind farm has an output of around 30MW.
https://www.offshorewind.biz/2017/12/20/developers-file-bids-for-powering-massachusetts-with-offshore-wind/?utm_source=emark&utm_medium=email&utm_campaign=daily-update-offshore-wind-2017-12-21&uid=69352
As a point of comparison, the only existing US offshore wind farm has an output of around 30MW.
https://www.offshorewind.biz/2017/12/20/developers-file-bids-for-powering-massachusetts-with-offshore-wind/?utm_source=emark&utm_medium=email&utm_campaign=daily-update-offshore-wind-2017-12-21&uid=69352