Upgrading RAM

Good Afternoon all,

I'm looking for some advice on RAM purchases.

Recently I've been thinking about upgrading my Ram, currently I'm using 4GB Ram ( http://www.newegg.com/Product/Product.aspx?Item=N82E168... ) and I'm thinking about buying an 8GB kit of the same model of what I'm currently using. ( http://www.newegg.com/Product/Product.aspx?Item=N82E168... ) so I can have a total of 12GB Ram. Since the Timing, and Voltage are the same for both kit, will I run into any problems with a 2x2GB and 2x4GB?
I do not plan on overclocking my system.

Or

Should I just go with a single 8GB kit and put the 4GB somewhere to collect dust? If so, can you guys please provide a link on what kind of 8GB kit I should get?

P.S. this is my motherboard ( http://www.newegg.com/Product/Product.aspx?Item=N82E168... )

Thank You.