Dave, you a bit wrong, the gain is tune on MIDIUM speed (to give gyro possibility work with high performance on low speed) until plane start oscillate, on max speed the GPS signal will decrease the gain. If the oscillate occured on maximum speed just need to increase the Speed factor in PowerBox "gyro setting menu" . Factory settings is "3" but can be encriase up to "5".
In these case the gyro will work with high performance.