CAS latency is very important and can distinguish expensive RAM from cheaper, higher latency RAM. The lower the number the better. CAS latency is a means to measure the time needed for the RAM to complete the following functions. In order to X-Y-Z
X - Precharge command to Active command. Charges the memory's storage capacitors to prepare them for data
Y - Active command to Read command. Selects rows and columns in memory array for reading
Z - Read command to Data Out. Reads data from selected rows and columns for transmission
The RAM you speak of is known as CAS-3 (Column Address Strobe) latency RAM. When the RAM is a lower latency you will notice a significant performance boost. For example:
Considering CAS-3 RAM running at 133mhz, it takes 45ns (3 clock cycles) for this ram to perform the given task. If you replaced the CAS-3 or CL-3 RAM with CAS-2 or CL-2 RAM that runs at 30ns per task you would see a 34% higher performance boost using the CL-2 RAM.
Hope that clears it up for you. I'll check this thread again if you have any questions.