Please report bugs here. If you are unsure whether something is a bug or an expected behavior, please post it on the "Technical Support" forum instead, and wait for a moderator to handle/move the post.
Yes, we have a regression related to the performance of the built-in datagrid, and we plan to address it.
In the meantime, you have these options: - Set the PageSize in order to reduce the number of items visible on screen at once - Use the wrapper for the Kendo Grid, which has great performance even for thousands of items, and which is available at: http://cshtml5.com/extensions/kendo.aspx