$700? How about "no".
For $700, you can get the fastest single gpu card on the planet, the Galaxy GeForce GTX 780 HOF Edition:
http://www.hardocp.com/article/2013/08/14/galaxy_geforce_gtx_780_hof_edition_review/
http://www.amazon.com/dp/B00DZIFN4M/
When overclocked, it will match (and sometimes beat) the performance of a GTX 690 or Radeon HD 7990, but without any of the problems associated with dual-GPU setups. I cannot stress this enough: Single GPU >>> multi-GPU.
Before you ask, the answer is: No, you cannot take any regular GTX 780 and overclock it to the same levels as the HOF edition card, since the chip used in the HOF card was especially binned for higher overclocks and the card itself is heavily modified to handle much higher voltages and heat without degradation.