8gb+4gb or 3x4gb ram?

[masteranu]

I have 4gb ddr3 1333mhz and
Intel i5 2400(only support upto 1333mhz)
I want to achieve 12gb
My mobo will be b75 which have 4 ram slots
What should i do?
Use 3x4gb or
With my current ram buy another 8gb?
Will there be any performance difference in gaming?

Fyi:Well its little bit hard to find 1333mhz 8gb ram for me

 

[masteranu]

I haven't bought mobo yet
I only have i5 2400,gtx 670 and 4gb 1333mhz with me