Hello Evgeniy,
Have you tried to ajaxify the multi-month view calendar using RadAjaxManager or RadAjaxPanel? Thus should speed up the performance of the control since the month navigation will be performed with ajax requests instead of plain postbacks.
You may also migrate to the latest
Q3 2008 Beta release of RadControls for ASP.NET AJAX which introduces optimized rendering for RadCalendar.
Best regards,
Stephen
the Telerik team
Check out
Telerik Trainer, the state of the art learning tool for Telerik products.