RAM: 8GB single module vs 8+4GB dual

[Psionic7]

So a friend of mine has a realy budget gaming rig.
AMD Athlon 860k as CPU, GTX 1050 on a Biostar Motherboard
Right now he is using a single module of 8GB HyperX Ram at 1866hz.
So the question here is it compatible to use the 4GB of the same company, with the same clocks and CAS, so he can have a total of 12GB running as a dual channel ?
Searching the forums i found that only 4GB + 4GB are gonna run as dual , the rest 4GB as single.
Is this gonna have impact in the gaming experience ? Better than it is now or worse ?

By the way, 4GB of RAM is easier to get cause its a lot cheaper than the 8 one,here where i live

 

[colelouiscloud]

Searching the forums i found that only 4GB + 4GB are gonna run as dual , the rest 4GB as single.

This is correct. Only sticks of the same size will run as dual or quad channel memory and if your motherboard has more than 2 slots, they have to be placed in certain slots or else the bios will disable dual channel. Which it will then turn back on when it actually sees dual channel sticks in the right slots. you can add a 4 gb stick to an 8 gb setup, but all that will do is increase the memory. No speed difference or dual channel will take place.