Hello Praveena,
Thank you for posting in the community.
In order to improve WebDataGrid's performance when a larger number of records are loaded, I would suggest enabling the Paging and/or VirtualScrolling behaviors. This would loading only a set number of records at a time in the grid, therefore easing the load:
http://help.infragistics.com/doc/ASPNET/2013.2/CLR4.0/?page=WebDataGrid_Behaviors.html
Regarding WebDropDown opening slowly, it would help to know how many items are loaded in the control and whether a DropDownProvider is used, or a template column with a WebDropDown. You may also be interested in WebDropDown's load on demand capabilities in this scenario:
http://help.infragistics.com/doc/ASPNET/2013.2/CLR4.0/?page=WebDropDown_Load_on_demand.html
Hope this helps. Please do not hesitate to contact me if you have any questions.