Can I used different sized ram kits together?

Solution
you can, but it may have some incompatibilities even though they have the same timings. Even filling up 4 slots of ram may see the need to decrease timings/speed for stability. Just remove the 2x4 kit and install the 2x8 kit for optimal stability and performance.
you can, but it may have some incompatibilities even though they have the same timings. Even filling up 4 slots of ram may see the need to decrease timings/speed for stability. Just remove the 2x4 kit and install the 2x8 kit for optimal stability and performance.
 
Solution