If you MUST have all four DIMM slots in play, you would be wiser to use the four Hyper X DIMMs so long as they all came together in one set. If they didn't, then it's much the same as mixing them with the Ballistix memory, as they won't have all been tested together for compatibility and it's going to be a crap shoot either way.
Please read the second section, titled "The odd man out or mixed memory" for further clarification on what is or is not possible/likely when mixing higher speed memory (Or any memory for that matter) together.
In the beginning, there was......BIOS Before you go ANY further, go to the manufacturer product page for your specific motherboard model AND revision. Revision is an important aspect because for any given motherboard there may be more than one version of that model which will be identified...
Also, if those four Hyper X modules did NOT come together in one set, if possible, it would be a good idea to try and figure out which two DID come together in a set, so that you can set them aside in sets in order to put one set that did come together in the A2 and B2 slots and the other two together in the A1 and B1 slots. Or so that if you mix them with the Ballistix kit, you can at least end up with two matched DIMMs from the Hyper X DIMMs together in there with them to increase the chance of them working well together instead of ending up with memory from three different kits all in the same machine. That's generally a recipe for problems even if they are only the occasional unidentified error that drives you nutty.