Hello Dmitry Shapiro,
We targeted performance in our latest release Q3 2008 SP1 and we will continue working in this direction. However comparing our controls directly with WinForms controls is most of the time not possible since most of the standard toolbox controls simply wrap the OS controls with unmatched loading time and painting performance. On the other hand as it comes to data-binding performance our treeview, virtualized combo and grid load faster than the toolbox alternatives.
Also they offer different level of styling and features - we provide rich and dynamic graphics (gradients, animations, etc) and style customizations at almost any level.
Nevertheless, I can assure you that we will continue working on providing better performance.
Do not hesitate to write me back if you have more questions.
the Telerik team
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