How to configure EKF for 20Hz GPS

Septentrio AsteRX-m2 and other SBF GPSs output data at up-to 100Hz
The device driver configures the GPS to 10Hz.

Should the EK2_GPS_DELAY parameter be changed to 110ms ?
How can I measure it ?

Can I change the device driver to ask for 20Hz, or are there side effects that I need to take into consideration ?
The device can do 20Hz, why was that not selected in the first place ?