THey aren't necessarily better than the 9 series its just people are having a hard time adjusting. Intel has huge heat and power consumption issues and they have locked OCs. People also didn't like being forced into PCI-E and DDR2.
The 875 and 865PE are classics, they were the dominant chipsets of the time, and extremely fast.
The 875 is basically and 865 with some added features and some performance tweaking. They are very nice chipsets. I would venture to say 5-10& faster is fairly accurate.
Hte 9 series are faster than the 8 series now, they weren't before because Prescott hadn't scaled up the clockspeeds yet. Also DDR2 is just beginning to become affordable and offer real improvements over DDR1.
-Kevin