If you are talking about CAS3 to CAS2 from 7 to 10% increase.
If it's from PC100 to PC133 then expect a 10% to 12% speed increase in memory performance.
What does this mean? Well in games a noticable difference. Thier smoother.
In business applications , you won't notice a difference at all.
Better memory does however give you a better chance at increasing your bus speed, therefore overclocking your system.