And what Crashman is getting at is that AGP PRO isn't necessary, which answers your first question.
As for using an 8X card in a PRO slot that works too. AGP PRO slots are made to handle the extra power of WORKSTATION cards, not any card that has 'pro' in the name, in fact I don't know of a recent proffesional workstation card that does have 'pro' in the name.
Workstation cards are like the 3Dlabs Wildcat series, the nV Quadro series, and the ATI FireGL series of cards.
So to clear it up further, the ATI R9800Pro will work in a regular 4X AGP slot, 8X AGP slot and a 4/8X AGP PRO slot; but an AGP PRO slot is not NEEDED nor even recommended really.
Basically the 8X AGPPRO slot is just an 8X AGP slot with more power capacity (50W or 110W depending on type). And you will still need to plug in the extra power cable for the R9800 even with the greater potential at the slot, because that's the way the card is designed.
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