I would sell it if I were you. $350 is a good place to start. If it doesn't sell within the time you would like, go down $10 each day until it either sells or you reach the minimum amount you would want to sell.
*Depends though, would you get a GTX 1070 or better from Nvidia, or would you want to wait until RX Vega releases? Because there isn't anything better from AMD right now.