The Effect of the Motherboard's Bus Speed on CPU Speed:
A computer motherboard's bus speed has no effect on the installed CPU's speed. In a computer, the motherboard and the CPU are two separate components and do not alter how well the other one performs. However, the user experience is measured in how well the two perform together.
CPU
The CPU, or the computer's main processor, has a factory-determined operating speed. The processor's speed can be altered through the motherboard's BIOS settings on some computers. Hardware compatibility errors aside, the CPU's speed is not altered by any other part of the computer. However, the CPU is the fastest part of the computer and often gets held up by other hardware that can't keep up. CPUs handle all the computer's computational work outside of major graphical work performed by the GPU.
Bus
The motherboard's bus is the part of the device that transfers data between parts. The term "bus speed" refers to how quickly the system bus can move data from one computer component to the other. The faster the bus, the more data it can move within a given amount of time. The system's "Front Side Bus" connects the CPU to the computer's "Northbridge," which handles communication between the computer's RAM and the processor. This is the fastest part of the bus and handles the computer's most vital workload.
Bus Feeds the CPU
The CPU itself is pointless unless it has data to process; the bus’s job is to get that data to the CPU. The bus does not increase or decrease the CPU's speed but handles that data that flows in and out of the device, which plays a key role in how well the CPU performs. This is the point where the Bus can affect the CPU's performance output -- the CPU works in a cyclical process, with data going in and out of the device on a timed interval. If the CPU doesn't have any data to work with in a cycle, it wastes a cycle and doesn't process any data.
Insufficient Bus
An insufficient bus speed could leave a computer's CPU hanging as it waits for more information to process. This creates a "bottleneck," or the point at which one part of the computer slows down performance for another part of the system. If the bus is too slow, the CPU will waste a substantial amount of cycles and the computer user would perceive this as slower performance.
Sufficient Bus
A motherboard that has a sufficient or excessive bus speed for the CPU will offer the optimal performance speed. If the bus is fast enough, the CPU will consistently have new data to process ready to go when it completes a cycle. While the process isn't perfect and there always being unused cycles, a sufficient bus speed helps maximize how many of those cycles are used.
<span>Source: http://smallbusiness.chron.com/effect-motherboards-bus-speed-cpu-speed-70907.html</span>