I would get the ASUS GTX 780Ti DCUII http://www.amazon.com/gp/product/B00HSY1RVC. The costs of 780Ti have dropped quite a bit lately and if you choose to upgrade later to the 900 series you should be able to sell the 780Ti for almost what you paid for it.
The rumors are $500 for the GTX 980 but nothing official, but I wouldn't expect it to be too much more than the GTX 780 it is looking to replace. And like I said it might drop the prices of the 700 series.
I would get the ASUS GTX 780Ti DCUII http://www.amazon.com/gp/product/B00HSY1RVC. The costs of 780Ti have dropped quite a bit lately and if you choose to upgrade later to the 900 series you should be able to sell the 780Ti for almost what you paid for it.