new pc question

[Pycno]

I dont think you need to RMA anything, aim for using specified speeds instead
With your board, occupying two slows on each channel, I would see how 1333mhz at cl9 worked.

Dont think of it as running the ram any slower btw, your 12gb ram is lightyears faster then any 6gb kit in situations where you use 6gb+. Even the fastest 6gb kits will make the entire computer turn into a crawl if it needs to borrow the hard drive due to insufficient ram.