Basically, there is no strict limit/number for the DataPoints rendered in the chart control. There are two general rules to keep into account. First, the larger the numner of datapoints, the more this is going to hurt performance. Having thousands of datapoints is likely to result in a slower chart.
Another thing to keep in mind is the visualization of these points. With a large number of datapoints, it is increasingly harder to visually distinguish among them - thus it makes sense to render fewer points. The best option is to test your speed and layout locally, and determine what number of points is most suitable for the particular layout.
the Telerik team