I wasn't really ranting because of PCI (PCIe has no big advantages yet - for desktops), but because of PCI interconnect, ie the connection from the north bridge to the south bridge and everything else.
It limits the complete I/O throughput to an absolute max of 133 MB/s in total.
gigabit ethernet requires 125 MB/s
(P-)ATA requires 133 MB/s
SATA requires 150 MB/s
So each of these maxes out PCI alone.
The VIA686B south bridge is complete crap; when PCI is saturated, it starts losing data from the IDE interface. All PC boards with this south bridge suffer more or less from this, causing massive instability.
When I was talking about PC133 that included the slow FSB and AGP connect. PC133/FSB133 can't do more than 1 GB/s (very theoretical value), so heavy AGP load slows down the CPU and vice versa.