You could create a custom ItemTemplate that displays the values of multiple properties in the data objects. To enable the text search of RadComboBox, however, you will have to create an additional property in the data object, that will combine the values of all needed properties. Then use the telerik:TextSearch.TextPath="the name of the new property" attached property to let RadComboBox use the new property.
The problem is that currently RadComboBox does not support filtering when its panel is VirtualizedStackPanel and this panel is needed if you want to display more than several hundred items without sacrifising performance. Attached is an example, that demonstrates how to create custom filtering, that has very good performance and behaves the same way as Google suggest. Please, note that you should unload the WPF project if you want to compile the Silverlight project and vice versa.
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