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Getting 2x card instead of 1x dual GPU card is always the preferred option unless you fall into a specific set of criteria. One of them being borderline craziness
Only kidding on the last bit but 2 cards is much better for heat and noise (and price!).
Unfortunately, the GTX 690 and HD 7990 haven't been released yet or reviewed, so we really can't say one way or other.
Also, you don't get the problems with multi-GPU cards like high noise, a lot of heat output, high temps, poor overclockability, reliance on multi-GPU scaling and possibly microstutter.