which timing is most important to least?

As you can see in my sig I am running 7 3 3 2.5....my question is this......which timing is most important to least importanr.....I listed these as they apear top to botom in my mobos bios.....2.5 being the cas obviously......I am purty sure that the cas is bar none the most important of all the timings...but which is second 3rd and fourth......the thing is my ram wont even boot at anything but 2.5 cas...for whatever reason I am not sure....but will changinfg it from 733 to 622 mean a big diff in performance?.....thanks a ton for the info

ker bump