8x is faster than 1x....its the purpose of the whole numbering system, to give you a quick idea about the bus capacity.
but bbrv is correct, its not the issue. there are few drivers for cards....there are few games to run on those cards....
people are going to run into many issues before they ever run into an issue about an agp bus bottleneck...
the most important thing, was having an AGP slot, because PCI cards are getting rare and limit your choices even more.
