Using all of my scholarly brain power I arrive at 609 which for intents and purposes is a useless date because nothing happened in that year which ammounts to any consensus within scholarship.
Neil ---
On the contrary, there certainly is scholarly consensus about what happened that year. It's recorded in the cuneiform tablet catalogued as BM 21901, popularly called the "Fall of Nineveh Chronicle." Nabopolassar marched against Ashuruballit, who was laying siege to Harran.
If you have the 2000 reprint of A. Kirk Grayson's Assyrian and Babylonian Chronicles, see pp. 95 -96, lines 58-75. If you're using James Pritchard's Ancient Near Eastern Texts, it's on page 305 of the third edition. I gave an URL for an online site last night.
Note that the entry for the sixteenth year of Nabopolassar says, in part, "the king of Akkad mustered his army and marched to Assyria" ... " he marched about victoriously in Assyria " ... "marched to Harran, against Ashur-uballit who had ascended the throne in Assyria." ... "The king of Akkad reached Harran and ... he captured the city."
Then, in the next year, the seventeenth year of Nabopolassar, the Chronicle says: "Ashur-uballit, king of Assyria, (and) the large army of Egypt ... crossed the river (Euphrates) and marched against Harran to conquer it... They defeated the garrison which the king of Akkad had stationed inside. When they had defeated it they encamped against Harran. Until the month of Elul they did battle against the city but achieved nothing ... The king of Akkad went to help his army ... he set fire to their ..." [Grayson, pp. 95-96, brackets removed].
[edited to say, see last night's message for links to a site with the text of the Chronicle ---
http://www.jehovahs-witness.com/10/87714/1557430/post.ashx#1557430 ]
Marjorie