I understand that Arria 10 has 3 speed grades (1, 2, and 3) and I am using a -2 part 10AS066H3F34I2SG. However, I see 4 timing models in the Quartus timing analysis tool (fast 900mv 100oC, fast 900mv -40oC, slow 900mv, 100oC and slow 900mv -40oC).
Do you know which model is appropriate for my part above?
All four are applicable to the part. The fast/slow represents the range of silicon that they have bundled as a -2 part and the 0C/100C represents the change in performance (i.e. switching speed) across temperature. In order to be reliable, your design needs to meet timing at all four timing corners.
Hope that helps,