I advised a client to not do this. They tried, failed and went with something else. I can't say I've seen it working yet.
In closing, there is no real payoff on DDR3 today. Why are you doing this?
I'm thinking of pairing 4GB of DDR3-1600 with a P5Q3 Deluxe, but when I research, there appear to be all sorts of issues with getting virtually any set of this speed of RAM and this mobo to play nice together.