Assuming you can get those 2 sold for those prices and you really want the 690 then I would try it out. If you are looking to use it, its always an investment but if you don't really care for it, then sell it. Nothing better right now on the market. Oh and shipping when selling cards will kill you haha.
The ones I looked at were close to 1k or more. I'm not sure what a card that costs that much does. I guess if you really worry about fps, statistics, and how much you can max to max games then it must be worth it. Because as more months go by they drop as something else is out.