For 500MH FSB (1000 DDR) 4-4-4-12 is a bit too aggressive for these modules.
I can easily do 4-4-4-12 running at 400MHz FSB @1T but that needs a slight bump in the NB voltage.
There is minimum real world difference anyway between CL4 and CL5, it's the higher C2D clocks that make the most difference.
Just run it at CL 5-5-5- 15/16/17/18 at 2.1-2.2v max, better to max out the FSB clocks than just low latency timings.

