2 x 4GB is definitely the way to go. Don't get stuck in a bad position in the future when you need to upgrade RAM, then the memory is out of stock, higher price, difficult to locate, etc. etc.
Future proof it now and don't worry about it again.
This kit is best:
F3-12800CL9D-8GBXL
With a single stick the system runs as single channel rather than dual channel. The memory architecture is not fully taken advantage of when using only one module.
Thank you
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