Adding 4gb single stick to a 2x4gb DDR3

[chazman113]

So one of my Corsair sticks died (CMX8GX3M2A1600C9) today and ordered a pair of "Crucial Ballistix Sport 8GB Kit (4GBx2) DDR3 1600" off Amazon (seemed to be the best deal). They seem to have the same exact timings. My question is, when I install the 2 new sticks, will I get a performance increase by keeping the 3rd stick in there single-channel. Could it possibly cause problems? Mobo is an Asus

 

[Calculagator]

The answer depends on how much RAM you actually use. The vast majority of people won't use more than 8GB. If that's you, you won't notice any difference having the extra 4GB. You may get slightly slower performance, but not enough to notice without benchmarking.
If you do actually use more than 8GB, you may get a performance boost on applications using large amounts of RAM.
Pretty much anything "could" cause problems, but it's very unlikely with a quality motherboard.