Different amount of RAM sticks or what will happen?

Question

RAM

Hello, tell me, please, does the PC have 4GB RAM, the second slot is empty, if you purchase a new 8GB RAM, install it, will there be a profit in this? read that if different manufacturers, volume, there may be some problems. I can’t say about the frequency of the RAM slot, I think that the purchased one will be higher. (1300 first, second at 1660), how will this affect the PC, will performance increase?
link to dxdiag, if you need to look at something on AIDA - tell me, I'll find out. I really need your help, thanks!