See that tab in CPU-z called *Memory* and *SPD* that would have been a good set of screenshots to include, but as you've stated its cas 4 I'm guessing its 4-4-4-12 memory that runs at 400MHz (DDR800). If you manually set the memory to 5-5-5-15 is will be very relaxed and shouldn't cause you any problems when you raise the FSB especially if you have raised the voltage from default 1.8vDimm.
What voltage have you set in BIOS for that screenshot pls, and what is the vDroop like at stock (idle/load).
Can you lower that vCore anymore?