It would all depend on the sticks. What are the voltage and timing specs for both? You are going to be limited by the lower rated stick. For example: If one is rated at 1.8v and the other is rated at 2.0v, you would either be pushing the lower one too far or under-volting the higher one. If they are close, you may be able to get something.
edit: the same goes for the speeds. If you are mixing a 667 with an 800, it will default to 667.
edit: the same goes for the speeds. If you are mixing a 667 with an 800, it will default to 667.
