Here are general guidelines to follow while "tweaking":
lower figures = better performance, but lower overclockability and possibly diminished stability.
higher figures = lesser performance, but increased overclockability and more stability -- to an extent
tRCD & tRP are usually equal numbers between 2 and 4. In tweaking for more overclockability, lower tRCD first between these two
CAS is not most critical of the various timings, unlike what is taught by many.
In general, the importance of CAS when placed against tRP and tRCD is nominal. Reducing CAS has a relatively minor effect on memory performance, while lower tRP & tRCD values result in a much more substantial gain. In other words if you had to choose, 3-3-2.5 would be better than 4-4-2.0 (tRCD-tRP-CAS)
CAS should be either 2.0 or 2.5. Many systems, most nforce2, fail to boot with a 3.0 setting or have stability problems.
tRAS should always be no less than the sum of CAS & tRCD – see below
tRC is usually no less than the sum of tRAS and tRP. So if you have a tRAS of 11 and tRP of 2....then tRC should be 13. tRFC should be tRC + 2.

tRAS is unique, in that lowering it can lead to problems and lesser performance. tRAS is the only timing that has NO effect on real performance, if it is configured as it should. Sure a high tRAS on the nForce2 chipsets shows a better sandra score. But real-life performance is the same with different tRAS settings as long as tRAS is no less than the sum of tRCD and CAS Latency. Lower than this sum, can and will negatively affect your system's performance.