Your memory settings are on Auto, right? If so, what is happening is that the motherboard is reading the contents of the SPD chips on the RAM. The SPD chips are programed with the RAM frequency, timings, and voltage so the BIOS can automatically set the RAM parameters. Your BIOS is telling you that you have DDR3-1333 RAM.
What you bought was RAM that was tested to run at 1600 MHz (400 MHz FSB freq) at some higher voltage and lower timings after it left the production line.
Do you plan on trying to overclock? If so, you need to adjust the RAM clock downwards to 1066 MHz. Increasing the FSB freq to 333 MHz will give you a core speed of 3.0 GHz and a RAM clock matching the SPD values of 1333 MHz.
Also, it gives you a 1:1 FSB:RAM ratio. Running RAM faster than the FSB in a Core2 system has little practical effect on system speed. The main thing it does do is contribute to instability, the last thing you need when you are overclocking a system.