Currently we offer 2 charting solutions for the Silverlight platform - RadChart and RadChartView (represented by the classes RadCartesianChart, RadPieChart and RadPolarChart).
The RadChartView is the newer control which addresses some of the limitations and deficiencies that we have identified in the RadChart implementation over the years. It is easier to set up and has vastly improved performance.
By migrating your application to RadChartView you should notice a significant improvement in performance and responsiveness. Have in mind that the two controls have very different architecture and not all features are supported by both of them.
For detailed comparison between the two controls, you can check this help topic.
I hope you will find the RadChartView control suitable for your project.