Best way to reduce flight controller computational load

With the recent post regarding high computational loading causing aircraft twitch, I looked at the loading of my CUAV-V5 for my heli. It is flying Copter 4.1.5. It uses EKF3 for two IMUs and one harmonic notch attenuating 3 harmonics. the computational load runs around 65 to 78%. I looked at reducing the number of EKF instances and switch from EKF3 to EKF2. Only running one EKF3 instance reduced the load to around 50-55%. Running 2 instances of EKF2 reduces the load to 45-50%. So my question is whether I should only run 1 instance of EKF3 or 2 instance of EKF2?