Speed is the frequency at which the memory works..for the example you give lets say PC3200 running at 400Mhz (effective)
The numbers you refer to are the memory timings which are the number of clock cycles needed for certain actions.The faster the speed and the lower the timings the greater the memory "bandwidth" or performance.
Generally the lower the figures the better.
So 2-2-2-5 is quicker than 3-3-3-7 because it can execute more instructions per clock cycle when running at the same frequency.
Slightly more technical explaination click here