No matter how fast your CPU is, it can't perform any calculations if it doesn't have any data to manipulate. It might be wiser spending the money on more RAM or a faster hard drive. Strive for some balance in your life. The video card converts the digital signals inside your computer to analog signals that your monitor can display. Various graphics accelerator cards exist to speed up your graphics display.
More memory is generally better, but different types of memory exist.
The CPU only manipulates data. Once your computer is out of physical RAM, the data is read from your hard drive. The speed difference between how fast data is fed into your CPU is typically 70 nsec for RAM and 10 msec for your hard drive. Even if you've got the newest 200 MHz Pentium, the speed improvement over a 60 MHz Pentium is only 3.3 times . It doesn't take Einstein to figure out which is more important if you're really interested in speed and performance.