RadChart will have problems with more than 1000 items on screen. While the product was designed to be easily customizable and feature rich it does not cope well with extremely busy charts. The control is targeted for casual situations which do not require a high performance solution -- usually several hundred points would fit on a normal display but with more points the details are lost anyways. There is a trade off to make between high customization and high performance and we've gone the rich features path as it is what most of our customers are interested in.
Here are some suggestions that should improve the performance in this case: Turn intelligent labels off. Actually, I would suggest turning the labels off altogether, as they would hardly be readable. Next step would be to combine several adjacent points into one e.g. take the first 5 (or so) values, calculate the average and add a single ChartSeriesItem using the average value.
the Telerik team
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