Nobody will be able to tell you for sure that you won't have problems, but the chance of such is small. I added 2 x 4GB to my computer recently to make it 16GB and didn't have any issues with it affecting overclock or anything else. The maximum stable-for-everything OC I can obtain on my 4770K is 4.3GHz (@ 1.272 Vcore, poor chip/IMC whatever), whether with two or four memory sticks.
The one time (with another build) I thought 4 x 4GB had problems and I asked here for help with SA voltages etc, it turned out to be faulty RAM in the end.