However, you have spent eight times as much on line drivers and receivers, and on the copper to interconnect them. Might be nice to load it in something less than the life of the universe. Go, AGP, go. Since the old days of the standard serial port, technology has increased enough to transfer data very fast on a few wires. Parallel requires many wires that will suffer from crosstalk if not very well insulated and if run at such high speeds.
Serial is cheaper, smaller and less complex.
Nowadays, new serial interfaces are faster than parallel ones also. Check FireWire, Serial-ATA and USB 2.0. Serial has its advantages. Maybe when today's serial runs out of gas, they'll go back to parallel, but serial has a lot of headroom. I have to correct one point here.