Most performant way to graph thousands of data points with WPF?

I'd consider downsampling the number of points you are trying to render. You may have 50,000 points of data but you're unlikely to be able to fit them all on the screen; even if you charted every single point in one display you'd need 100,000 pixels of horizontal resolution to draw them all! Even in D3D that's a lot to draw.

Since you are more likely to have something like 2,048 pixels, you may as well reduce the points you are graphing and draw an approximate curve that fits onto the screen and has only a couple thousand verts. If for example the user graphs a time frame including 10000 points, then downsample those 10000 points to 1000 before graphing. There are numerous techniques you could try, from simple averaging to median-neighbor to Gaussian convolution to (my suggestion) bicubic interpolation. Drawing any number of points greater than 1/2 the screen resolution will simply be a waste.

As the user zooms in on a part of a graph, you can resample to get higher resolutions and more accurate curve fitting.

When you start dealing with hundreds of thousands of distinct vertices and vectors in your geometry, you should probably consider migrating your graphics code to use a graphics framework instead of depending on WPF (which, while built on top of Direct3D and therefore capable of remarkably efficient vector graphics rendering, has a lot of extra overhead going on that hampers its efficiency). It's possible to host both Direct3D and OpenGL graphics rendering windows within WPF -- I'd suggest moving that direction instead of continuing to work solely within WPF.

(EDIT: changed "DirectX" in original answer to "Direct3D")

Just ran into this question, but as I mentioned in this thread, the most performant approach might be to program against WPF's Visual layer.

Everything Visual in WPF eventually goes against this layer ... and so it is the most lightweight approach of them all.

See this and this for more info. Chapter 14 of Matthew MacDonald's Pro WPF in C# 2008 book also has a good section on it.

As another reference ... see Chapter 2 of Pavan Podila's book WPF Control Development Unleashed. On page 13, he discusses how DrawingVisuals would be an excellent choice for a charting component.

Finally, I just noticed that Charles Petzold wrote an MSDN Magazine article where the best overall (performant anyway) solution (to a scatter plot) was a DrawingVisual approach.