optimal output load

Dear all,

I am following the filter design procedure described in CN0227. This procedure describes an high speed ADC driver design using differential amplifier. At step 5 (page 3): " select the optimal total load seen by the differential amplifier "

How I can determine the "optimal load" of a certain differential amplifier (I am interested in particularly ADA4932, ADA4938, ADA4937)?  

Thank you for your help.

Best wishes,

Janos