you can't or at least shouldn't mix and match. the memory should be the same speed and preferable the same manufacturer and/or model.

the 10600 are faster but it may not be night & day faster, so if it doesn't cost too much go with the faster.
I personally found that corsair dominator's using an XMP profile worked better than the OCZ ... just my personal experience, i'm sure someone out there might prefer OCZ over corsair.