iDRAC firmware version will defer from generation to generation.
For 10G Modular server, latest iDRAC firmware is 1.65. 10G Modular servers include M600, M605, M805 and M905.
For 11G Modular server, latest iDRAC6 firmware is 3.50. 11G Modular servers include M610, M710, M915, M910, M710HD and M610X
For 12G Modular server, latest iDRAC7 firmware is 1.40.40. 12G Modular servers include M620, M520, M420 and M820