If you are going to use a stand alone video card with this system, you should save your money and stick to the 1600 memory.
If you plan on using the APU (built-in video adapter), then you may be able to take advantage of the 1866 memory.
Regardless, the memory rated at 1866 should run in the system, for the APU it can improve video performance, but not a huge amount.
Personally, I would recommend, for max stability and cost, that you just stick with 1600 memory.
Thank you. Looks like I'm in the good way. I do plan to use the built-in video adapter. Originally was buying a 1600 memory then the online store went out of stock so I changed for another (a better one) but I made a mistake and choose 1866 instead a 1600 wrongly.
Thank you very much!