How can a graphics card be optimized for WPF 'Dirty Rectangle' update rate

I'm trying to write an application to display multiple video streams, all updating at 25 or 30 images per second. The images are being rendered into WPF controls using Direct3D and some Interop to avoid using a Winforms control. As more video streams are added, the frame rate of each control drops yet the CPU on my machine only ever reaches about 50%.

Using the Microsoft WPF Performance Suite - Perforator tool, it would appear that when the frame rate on the video streams starts to drop, the 'Dirty Rect Addition Rate' levels out like it has reached a maximum for the video card.

There is no software rendering activity in the application so it would appear that overall performance is being limited by the graphics card's ability to update the Dirty Rectangles.

Therefore, is there a feature or performance parameter that can be used to determine the best video card to buy in order to maximise performance for my application? Either that, or is there a set of graphics cards settings that will boost performance? Currently running with an ATI FirePro V4800 that will happily run 16 streams of H264 video at a resolution of 4CIF but lo开发者_C百科oking for the ability to run up to 32.