Bit-Tech published an article on Overclocking Intel's Core 2 Quad Q6600

One comparison that we've made in the office over the last week or so since we started really tinkering with our Core 2 Quad Q6600 is to the Athlon XP 2500+ for those of you that remember that CPU. At the time, AMDs flagship processor was the XP 3200+, which was clocked at 11x200MHz. The XP 2500+ shared the same multiplier as the 3200+, but used the slower 166MHz front side bus speed.

Getting flagship performance out of the XP 2500+ was as simple as increasing the front side bus from 166MHz to 200MHz virtually every processor did that on stock volts. I think we're going to see something similar with the Core 2 Quad Q6600 it shares the same multiplier as the Core 2 Extreme QX6850, but uses a 1066MHz front side bus instead of 1333MHz.

Overclocking Intel's Core 2 Quad Q6600