Content DB Migration from 2010 to 2013

Hi All,

There's a need to split 1 Site collection with around 400+ GB data in one content database into 10 sites and we are suppose to do it as part of our upgrade from 2010 to 2013, I know the data is too huge to be in one content database and that too in SP 2010 but yes now we need to take the corrective action :) ...

What could be the best approach to do this using a reliable third party tool or any out of the box sharepoint feature and most importantly what kind through put I should expect (i.e thruput rate to transfer/move 400+ GB of data) let's say for around 1 GB of data.

Thanks ...