The Asus A7V8X gives the same or better performance as it's predecessor(when using DDR333). The features are well worth the extra $10.
Currently, DDR400 memory isn't as good as DDR333 memory, so use DDR333 memory with the board.
AGP 8X provides no real performance boost now, but when graphics cards start pushing the limits of AGP 4X, the picture will change.
Serial ATA is an excellent technology to get your hands on. There will likely be huge performance boosts with a Serial ATA setup. IDE devices are, after all, some of the slowest components on your system.
Pain is the realization of your own weakness.