[X4U] PCI or PCI-X Slots - which is better?

[coolcat at hostalive.com]

The Dual 2GHz PowerPC G5 has 3 PCI slots but the Dual 2.3GHz PowerPC G5 has
3 PCI-X Slots. 

Q: 
- Which type of slot is better?
- Do the PCI-X Slots accept older PCI?
- How many products in in either format?

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[db-lists]