Comparison of THD in Analog Multiplexers

Hi

I require an 8:1 analog multiplexer in a new design. Ideally a dual 8:1 multiplexer would be best & I am considering the ADG1407BRUZ, which I have used before. The THD spec of this part is given as 0.07% typical for RL=110R. Previously I had to lower my input signal in order to achieve the level of THD I wanted.

I am now considering using two ADG5208F 8:1 multiplexers rather than the dual ADG1407 part. It has a THD spec of 0.005% typical. However, this is into a 10k load rather than he heavier 110R for the ADG1407 device.

I would like to be able to compare the 2 specs in order to decide whether one part is better than the other. I understand that THD is related to RON Flatness, hence the reason I reduced my signal level previously.

Is there a way for me to approximate THD for different loads based on the Ron Flatness & Ron values, maybe an approximate formula? if not how can I compare the ADG1407 & ADG5208F in order to decide which part has better THD performance?

regards

Steve