Can I mix and match DDR2 with different voltages?

Question

I currently have:

Corsair 4GB (2x2GB) DDR2 800MHz/PC2-6400 XMS2 DHX Performance Memory CL4 2.1V

Would I be able to add to the system:

Corsair 4GB (2x2GB) DDR2 800MHz/PC2-6400 XMS2 Memory Kit CL5 1.8v

My reservation is that the sticks run on different voltages. I have an ASUS P5Q Pro board.

Answer 1

Never do above 1.65V thats insane. And dont mix the Voltages on ram dimms