The sticks are going to initially run at a slower speed and looser timings. They'll be running at the same speed, because it's not physically possible for different sticks to run at different speeds and timings on the same board. You can go into your BIOS and set the memory timings and speeds manually. I personally would set them to the slower of the two sticks and see if they run. Since you can't set individual sticks, you'll be setting both of them at once and they'll run at the same speed. It's a pretty normal thing to have to do anyways even with sticks that are sold together in a kit because they often boot up initially with slower timings than advertised.
Once you do that, it's overclocking memory as normal. You'll probably be limited by the slower of your two sticks, but that's not much different than how it normally works. Be sure you know how to reset CMOS and do some homework before you attempt that. But you should be stable up to the slower of the two sticks' clocks.