So, I've been playing..
http://stargazerslounge.com/topic/218697-atik-titan-gets-a-17fps-realtime-registration-test-d/The titan is pointing at the screen without a lens. The computer is capturing each image, uploading it to the GPU (graphics chip) and then using the graphics chip to perform image alignment for realtime stacking.
At 17FPS, it means each image is taking approximately 0.057 seconds to process. The 383L images are fast too.
Once I have time, I'll set this up with a scope and take another video - hopefully realtime solar/planetary stacking!
The code is not optimised, it's also processing LRGB as greyscale so there is a possibility I can get this running at 60fps for mono cameras.
The link also shows my original CPU based routine that, when optimised, took 4 seconds to align a 383L image.