The Bus Speed is the actual frequency, that the FSB is running at. The Rated FSB, is the real effective frequency of the FSB, since the FSB of Intel processors, are quad pumped, to increase it's efficiency.
Your processor speed is reading 1.6GHz instead of 2.4GHz, because it is throttling down to save power, when the CPU is not in use, or idle. To stop this, go into your BIOS' advanced menu, and disable C1E and EIST. These are power saving features, that throttle your CPU's speed down, to save power.