Remember that a high processor cycle rate is not much help if the FSB (Front Side Bus) speed is low, for example, using a P4 at 2.4GHz on a motherboard with 300MHz FSB. With current processors, the "glue chips" (FSB) that pass the CPU information back and forth to the memory and other devices are the real bottleneck. So putting a new processor on an old motherboard won't get you the performance you might expect. New motherboards have FSB of 800MHz and more, but that's still a whole lot slower than the CPU speed. So the CPU probably spends significant time waiting for the rest of the system to catch up - though HyperThreading helps keep it busy. Getting the fastest memory that your motherboard supports is also critical.