The columns swapping feature is a resource-heavy operation and it involves a lot of DOM operations. It is expected to be a little slower when you are using a lot of data cells (100 records).
However, I can recommend you to swap the columns on server side.
I hope this helps.
All the best,
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed