the extra slots are for use in pci-x slots, the |||| |||||||||||||| |||| layout lets the card work in a pci-x slot that provides higher clocks and voltege then normal pci slots, these are only found in server or veryhigh end workstation boards such as those made by tyan, but the card is a pci card just with the ability to work in a pci-x slot(64bit pci)
Actually the keys are for voltage, the layout you're showing supports both 3.3V and 5V. PCI-X has another small piece next to that. The key closest to the back of the case means the card can run at 3.3v, the second means it can run at 5v. Many cards can run both and hence have the layout shown by you.
PCI 3.3V
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PCI 5V
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PCI 3.3V & 5V
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PCI-X (3.3V & 5V)
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That Pinnacle card should be standard PCI, also it's not "for use in PCI-X slots" it's not like they're normal cards which have extra PCI-X functionality or anything, it's the other way around. PCI-X cards are backwards compatible with PCI if you're lucky. Not all PCI-X cards will work in PCI slots. Plus it's not limited to very high end stuff, crap workstation boards have it too, even some desktop boards, those are often limited to 66MHz though. It all depends on the chipset.