Can I use one graphics card for games and one for Bitcoin mining, without losing performance? I have a GTX660 right now, but I bought an R9 290x recently. I was wondering if I can leave both in my pc and use one (the GTX660) for Bitcoin mining and one (the R9 290x) for everything else (mostly games).  


Is this even possible?  
Will it decrease gaming performance to run a miner on a separate card?  


The rest of my specs:
i7 3820 @ 3.60 GHz
16GB DDR3 RAM @ 1333MHz
Asus 2011 P9X79 Pro
Windows 8 pro  

I bought the new card for gaming, but if it would be possible to do this with my old card without losing performance that would be great.
With the advent of ASICs, Bitcoin GPU mining is no longer profitable. I would recommend mining a Scrypt coin such as Dogecoin or Litecoin. (You can then trade it in for Bitcoin on an exchange, if you prefer.)

To answer your original question, yes, you can use one card for mining and the other for actually running the computer.