It's unstable. The ram specifications on the box are pretty much the highest stable settings tested for the kit. ANything with lower latency or higher frequency would probably require more voltages and you'll probably also need a bit more tweaking around.
Honestly overclocking RAM isn't really worth it. If you're gaming you probably will get only an extra frame out of it. If you're doing some video editing or rendering stuff, you might find that this'll be a bigger headache than its worth if you don't really know what you're doing.