I am unsure how to compare the settling times of the AD5544 and the AD5686, due to the different way in which they were measured.
The AD5544 goes from 0 to full scale then back to zero and has a settling time of 0.9us to plus/minus 0.1% full scale. The AD5686 goes from 1/4 to 3/4 scale settling to within plus/minus 2 LSB within 5us. How do I compare the settling times of these two DACs?
You may notice that these parts have 12 years difference in them and some methods and metrics of certain parameters change with technology. Another thing that may help you decide is by looking at the Typical Performance Characteristics section and look for the settling time graphs. If you want the one with the faster settling time, I would recommend the AD5544.
I'm moving this to the Precision DAC community where someone can answer your question.