The guys are right that what you're describing is a disaster, but not necessarily because the RAM is mismatched. With some minor tuning, you would most likely be able to get the system to run just fine with that setup. However, depending on how you install the RAM, it may not run in dual channel mode, witch will effectively halve your memory bus width. It's not like you'll have half the memory performance, but the system will definitely suffer because of it. On the other hand, the motherboard may be able to set up the two 4GB sticks with the 8GB stick to run in dual channel. It's worth experimenting...
This post has been edited by SnyperTodd: 26 February 2013 - 01:07 PM
Reason for edit: mispelling