Computers clock speed is determined by it's bus speed times the multiplier. For example a 200Mhz has a 66Mhz bus speed, so it's really a DX3 200. On this page you will learn what yours runs on.

The highest bus speed possible on a computer is 83Mhz (right now).

Clock Speed	Bus Speed
75Mhz	50MhzX1.5 or 75Mhz
90Mhz	60MhzX1.5
100Mhz	66MhzX1.5
120Mhz	60MhzX2
150Mhz	75MhzX2 or 60MhzX2.5
166Mhz	83MhzX2 or 66MhzX 2.5
200Mhz	66MhzX3
233Mhz	66MhzX3.5
266Mhz	66MhzX4
300Mhz	75MhzX4 or 66MhzX4.5
333Mhz	83MhzX4 or 66MhzX5

Warning if you push your bus speed beyond 66Mhz you will be risking the chance of ruining your stuff. The PCI bus is meant to be run at 33Mhz or slower. You will be runing over PCI 2.1 compliance if you go over that. Note that some later models like the 350 deschutes from intel will be the first to run on 100Mhz bus speeds, so that means the motherboards will slow down the pci bus while still using the bus speeds.