Hi,
Output voltage swing:
Generally I don't think that the simulation models are optimized to show realistic values.
Besides this your circuit differs regarding test conditions. The datasheet conditions are:
* RLoad = 10k ... usually this is against (VS+ + VS-) /2 = (+5V + 0V) / 2 = +2.5V.
* Gain = 1
* And it mentiones: "The AD8220 can operate up to a diode drop below the negative supply but the bias current increases sharply. The input voltage range reflects the maximum allowable voltage where the input bias current is within the specification." ... which may explain the knee.
Generally I believe more in datasheet values than simulation values.
Klaus