CoreTemp detected my CPU E6600 properly. I didn't overcloked it so the FSB is at 266MHZ. But the multiplier is changed through Intel Speed Stepping from 9x to 6x.
So CoreTemp assumes a higher fsb instead of detecting the real fsb. Here is a screen:
The clock speed detection clearly needs updating But I don't have the time to fully implement a change, as its a bit more complex than it may seem.
In the next version there should be a workaround for this, and hopefully it will work fine and detect proper speed.