1gb - Ddr @ 2.5

I'm running an NF7-S with 2 - 512 cas2.5 Corsair sticks of memory. I want to keep dual memory so I need a 1GB stick. It seems like Corsair only makes 1GB sticks at cas 3. I don't want to lose any performance. Does anyone know where I can get a Cas 2.5 1GB stick that will play nice with the Corsair I have now?

Thanks

If you get another 1GB stick and have a total of three sticks then you won't be running in DC. You need to have matched pair in order to run DC so keep that in mind. 2.5 Cas are hard to come by in 1GB sticks so far the ones I seen are from OCZ, Patriot and Mushkin but I don't think that Corsair has it.