Have you tried the CH6 stick on its own?
Test all sticks individually and see which one performs the best... from my experience, putting the best performing stick in Dimm3 and the other in Dimm2 will gain some FSB... but this was on a 2x512MB setup.
Also, try BIOS D10 if you'r not using SATA... like I said above, it helped me a bit... I'm 232FSB solid with D10 and 2-2-2-11 timings.