Any dual channel kit should be just fine. When it comes to ram speeds you really don't need more than regular 1600Mhz mem, you'll never be able to notice the difference vs say 2400Mhz ram. The only time you really need fast ram is for benching or if you just like tweaking and to have many mhz.
And 16Gb of 1600Mhz will probably be faster in windows than 8Gb of 2400Mhz, so I'd rather go with more mem rather than faster mem.
I know some people claim games run smoother with 2400mhz, that's just BS. For starters 2400Mhz really doesn't say very much about how fast the ram is, the timings of the mem are just as or more important.