We added in the Precision Grayscale mode to increase the resolution of the marker tracking, similar to OptiTrack, as you point out, but with a different algorithm.
The TIR5 grayscale mode slightly increases USB bandwidth usage, but not by very much, the overall data rate is still very low. Due to our implementation, we haven't measured any increased CPU demand. Yes, the OptiTrack V100 cameras are capable of computing the marker centers in the camera, and this is important when you have 24 cameras working on the same PC.
Yes, you can read in grayscale from the OptiTrack cameras, if you mean can you read in the raw uncompressed image. You can do it at 100FPS at VGA resolution.