The 9800 isn't really that overpriced- it soundly outperforms the Geforce 6600 thats 15-20$ less. However I will say that its power consumption isn't too efficient; it doesn't utilise any of the 12v rail.
I've got a 9800 XT in my rig and an X700 Pro 256mb AGP in another. There is almost no performance difference whatsoever, so it may be a tad bit faster than a 9800 Pro. The X700 Pro does seem to run cooler and use less power, and it probably overclocks better, but it's not worth the upgrade.
Are you trying to decide which to buy between these two? In that case I might go with the X700 if I wanted to stick with ATi, but I don't think the price ($200ish?) is really justified. I would reccomend the 6600 GT. Outperforms the 9800 XT, $150ish, and it's a newer card with some newer features.