The lower timings, the faster the memory is. A module with 4-4-4-12 is faster than one that is 5-5-5-12. However, if the bus speed on the former is 667mhz as opposed to 800mz in the latter, well that's reduced any impact the timings make.
With DDR ram the timings were critical for gaming systems. Corsair ram for example went as low as 2-2-2-11, but it was mind numbingly expensive and only the best systems could make it really work for them.
With DDR2 the timings are nowhere near as critical.
Tbh, whereas with DDR I used to really watch the timings, with DDR2 I just go for which modules will work best with the system, and value for money. As long as the modules are made by a good quality manufacturer all will be well.
I wouldn't get too het up over it.