those numbers are the number of clock cycles in which in RAM takes to do a certain task. I can't remember the actual names of the taskes. One of the most important in the CAS. The first number in the set. The lower the timings, the faster the RAM is at what ever speed it is rated for. For example:
DDR400 (PC3200) RAM with timings of 2-2-2-3 is faster than the same RAM with timings of 3-4-4-8.
Your theory that it effect overclocking is not entirely wrong, RAM with lower timings has a high chance of overclocking to higher speeds (but with slower timings).
When o/c you increase the stress on the RAM, to releive the stress (so the RAM runs stable) you losen the Timings from say, 2-2-2-3, to 2.5-3-3-8.
Underclocking the RAM relieves stress to the RAM, so you can tigten the timings to increase the stress.
Hope this helps
<font color=blue><font color=red>Milk</font color=red> my <font color=red>ass</font color=red>, and call me <font color=red>Nancy</font color=red>!</font color=blue>