You should settle for the 2x R9 290X instead of the 1x 780ti.
But make sure your case has proper cooling and your PSU is beefy enough to support these beast cards.
Your PSU will not be able to support 2 R9 290X's in Crossfire.
Here's the 2x R9 290X's.
PCPartPicker part list /
Price breakdown by merchant /
Benchmarks
Video Card: Gigabyte Radeon R9 290X 4GB WINDFORCE Video Card (2-Way CrossFire) ($545.99 @ SuperBiiz)
Video Card: Gigabyte Radeon R9 290X 4GB WINDFORCE Video Card (2-Way CrossFire) ($545.99 @ SuperBiiz)
Total: $1091.98
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-05-09 19:05 EDT-0400)
The PSU I would recommend for this would have to be atleast 700W, and you might want 750W in order to overclock each GPU and your CPU.
You actually might want to get a custom cooler for your CPU if you are running this setup too.
PCPartPicker part list /
Price breakdown by merchant /
Benchmarks
Power Supply: SeaSonic G-750 750W 80+ Gold Certified Semi-Modular ATX Power Supply ($94.99 @ Newegg)
Total: $94.99
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-05-09 19:06 EDT-0400)
It's great value for the performance you get our of the Power Supply.
Also, you might want to consider GTX 780 SLI, a GTX 780 is the equivalent to the R9 290X, so it might be viable.
It's cheaper and the 780 and R9 290X can trade blows all day.
PCPartPicker part list /
Price breakdown by merchant /
Benchmarks
Video Card: Zotac GeForce GTX 780 3GB AMP! Edition Video Card (2-Way SLI) ($476.99 @ SuperBiiz)
Video Card: Zotac GeForce GTX 780 3GB AMP! Edition Video Card (2-Way SLI) ($476.99 @ SuperBiiz)
Total: $953.98
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-05-09 19:09 EDT-0400)