Corsair has a RAM selector on their website where you can enter the mobo model and find the appropriate RAM that works. The mobo maker QVL list only shows what they have confirmed to work - usually when the first mobos are released. A RAM mfgs. website is likely to be more up to date.
I would NOT suggest mixing of RAM even the same part number DIMMs as they are not guaranteed to function without issues. DDR2 is less sensitive than DDR3 due to a lower frequency but RAM is relatively cheap right now so I'd buy ONE matched, tested RAM kit and be done with it.