Chris, can I suggest something?

Can you make a visual indicator on your teststand for throttle movement? That makes it easier for us to judge how well the engine follows the throttle.
I am saying this, because a lot of videos out there (especially the ones from Morris Mini Motors) show engines that APPEAR to have a snappy throttle response until you enlarge to full screen and watch the relation between engine RPM and throttle movement.

Just a thought.

I myself am planning to fit a 2nd servo on the teststand that has no other function than to move a big dial indicator so the throttle position and movement are clearly visible in the video.