I had this working in Silverlight about 2 years ago using a sample provided by Graham Murray but that sample does not seem to work the same in the WPF XamDataChart. Before I try to make the modifications to get this to work I wanted to see if anything has been added that enables this to work efficiently?

Right now it is implemented as a behavior that attaches when the mouse enters the chart,  it takes the current x position of the mouse and translates that to a datetime based on the x-axis. Then for each series it find the closest element in the itemsource to that datetime and adds them to a collection thenthere is a separate behavior that displays that collection in a tooltip style. The only problem Ihad with this method is if there are a lot of points in each series the looping take a while and everything becomes choppy. 

Is there a better way now?