very important !
in the category Ram Clock not only needed but still there are CAS, RAS, TRC etc. Of course, most high-Clock will be FASTER BUT have to look at JEDEC standard, you can see it in CPU-Z.
For example: 6-6-6-15 (clock 400MHZ) with 9-9-9-27 (clock667MHz) will be the same speed. so we can not conclude a high clock will be faster than a low clock without looking at the CAS RAS, TRC timming of RAM etc.