PCI was before AGP, then there was AGP 4x then AGP 8x. If you use a AGP 8x card in a AGP 4x slot it's going to only run at half the bandwidth.
PCI and AGP are older and MUCH slower than PCI-E.
Newer computers (after 2005, lol) use PCI-E, not AGP or PCI.
So the answer to your question is no. If you have an AGP slot, there is no point in getting a PCI card.