$450 in my opinion. Ether is the second best coin. Looks like its following bitcoin after turmoils in markets. So it is safe bet to say it will $100 more. 500-600s are quite high. Might be!
Ethereum has just Hard fork success, I think Eth will rise again. But it will not grow too fast because Eth is relatively stable and long lasting.
So it suits those who want to keep long! And do not want to risk their money.
Eth will reach $ 500 - $ 600 and grow slowly until 2018!