I'VE FOUND THE SOLUTION!!!!
The main reason that databinding a datatable to a grid is so slow is because the drawing of the columnnames takes alot time. The simple line of code:
gridHeader.ColumnHeadersVisible = false;
Speeds up the databinding process from
180-300 ms to
4 ms!!!
Now this might not be a good solution for you because the tablecolumns are quite important for the showing of data, but for me it's not a problem as I already create some custom controls that I place over the column names. So by disabling the column names, my own column-name-controls remain present and give the user insight in which column is what.