I wonder how this would fare as the basis of a new tracking system combined with FreeTrack...
http://viewbits.com/color-megapixel-CMOS-camera.html
or
http://www.ehd.de/products/cmoscameras/usb2cmoscameraskameras.htm
(SMX-160)
For starters, FPS looks decent enough at 640x480 (126).
(for reference, TrackIR 4 PRO works at a software enhanced 358 x 290 and 120 fps)
Cheers!
EDIT: price information coming up..