The xamDataChart uses all WPF/Silverlight retained mode graphics for all rendering, at present, so achieves speed oftentimes by virtualizing the visual so that it represents the data well, but doesn't display information that you can't percieve visually.

With a scatter/bubble chart such as this it tries to remove uninteresting points (obscured points, etc.) down to meet the maximum marker limit. The visual virtualization it performs here unfortunately often intrudes into the realm of perception as its much easier to tell with this type of chart that you are being presented with representative data rather than the full set, visually.

If you set the maximum marker limit to be very high it will show you all the markers, but you also end up pushing the Silverlight/WPF engines far outside the bounds of what it wants to deal with. The point markers are full fledged ui elements and there is a severe cost with addding so many of them to the layout tree, thus you will experience quite a delay if you choose to display that many.

For your scenario, you really need some lighter weight rendering to be associated with each marker than is possible in Silverlight without much more engineering. It is easier to achieve in WPF, but thusfar the DataCharts focus has been on platform parity. If this is an important feature to you, please make a feature request, and we will see what we can accomodate.

If you have version 11.1 installed, you could experiment with the UseLightweightMarkers property as this will cut out some of the overhead that we introduce to laying out the markers (self-centering, color binding). But if you turn on this mode, you will need to create a marker template that self-centers itself and has a static color assigned, rather than acquiring its color through data binding. But, in the end, this can't eliminate the fact that WPF/Silverlight do not want that many UIElements attached to the layout tree at once. Your best bet is to request a version of this series designed to use a lighter weight rendering scheme for the markers: