If anyone using Telerik controls is facing performance issue, then you can get the desired performance by doing small changes. Basically RadControls(I have mainly used RadGrid) creates a large amount of viewstate on every page(Which is used to Store the data related to RadGrid functionality such Paging,Expand State etc) and which also takes up additional resouces. But If you want to use the functionality you can’t disable the viewstate.
So the best solution I found is using RadCompression to Compress the viewstate. RadCompression provides a lot of functionality like compressing viewstate, moving the viewstate to session etc. and the best part of this technique is that we even don’t need to change the code. Just we need to make some changes in the config file.
For more details please go through this link “http://www.telerik.com/help/aspnet-ajax/compression.html”
I have used this in my page and it worked. It has reduced 50 Page viewstate to 4 lines.