Mixing RAM is not good, I tried it with Reapers and OCZ Platinum for 6gb and it worked for a bit then memory errors like mad (all slots and RAM were fine however)
Can you not sell both sets and go for 2x2gb instead?
I could but I really dont want to, my rig seems working fine and I cant see any problems at the moment, I got ram at stock and its fine, its not even been pushed, been playing games etc.. aswell no probs.