I can run rawopint now with 1100ms intervals without error (40 shoots).
Is this build really faster or is just calculation of sleep now correct?
I expect it's actually faster. The sleep calculation is just a difference between clock values, so there's very little chance it was wrong.
That doesn't mean the camera is actually running faster, it just means that the way it was before ended up wasting time somewhere.
To maintain a set interval in continuous mode, rawopint needs to stop the shooting process until it's time to take the next shot. This is done using the remote hook, which normally is very close to where the shot actually starts. In the original g1x port, this was in a different place, quite far from where the shot starts, which appears to have had some side effects. The Canon firmware doesn't expect to be stopped at any of these points, so side effects aren't surprising.