Explicitly update a table after sp_tableoption "text in row" advices wanted
Sounds to me you're missing indexes for the queries your application actually uses. select ntextcol1, ntextcol2 from table takes 5 min is not the point: this is a table scan that retrieves all LOBs. Your application (hopefully...) never issues this query. Pulling ntext (you should be using `NVARCHAR(MAX) btw) in row or pushing them out of row is not what you should be looking at.

Read General Index Design Guidelines and all the related articles in the section (clustered index design guidelines, non-clustered index guidelines etc etc). And learn how to identify the problem queries in your app, the indexes should target those queries: Troubleshooting Performance Problems in SQL Server 2005, Waits and Queues