These I just had lying around actually
I have not analysed what causes the drift yet, other than it seems to be the sensor going to far in one direction compared to how far it's physically moved. Some tuning might be possible.
1. 11 inches pr. second. Not very fast, but decent (accuracy may suffer though).
2. Everything should be pretty flat, but I'll take that into consideration on the next tests, to make sure the mouse isn't ever so slightly tilting because the grabber lifts it.