RAID 0 performance gains?

Hardware-RAID-0 is always faster than a single drive because you can step the reads and writes across the two drives simultaneously. Downside is that if either drive fails, you lose data on both disks. So if your backups are good, and you are willing to take the risk of a slightly higher risk of data loss, go for it.

Software-RAID-0 can provide improvements, but in my opinion not enough to justify the increased risk of data loss. Also, you almost can almost never boot from a software-RAID-0 partition.

Wasn't there an article recently that had an obscene number of TB drives in a stripe to see how the performance compared?

Don't do this. Instead of buying one of those TB hard drives, buy a western digital raptor or velociraptor drive. It's small, yes, but you don't need to put THAT much content on your main system drive.

What you get are latency and transfer speeds that far exceed what two large TB drives will ever be capable of. Even though the throughput from raid is pretty high, you still have to have one of your two drives find the start of a file before it can begin playback, meaning that for many smaller files, or when you're accessing lots of different files, as during startup, your raid array is not speeding things up substantially. Furthermore, it might even be degrading performance, depending on your read/write problem.

Go with a fast 10k rpm drive as your system drive for the things that need to be fast, and use a big drive for media storage. They're different tasks, use the appropriate hardware for each.

I'd buy an SSD and put my OS and programs on that, and use the disks for data storage.

You need to carefully consider the overall system rather than just focusing on one piece at a time.

Unless you are already going all out on your other components, you'll probably get a much better performance gain by putting your money in places other than RAID 0. Memory (Size, not so much speed), CPU & GPU will all likely be much better bang for your buck.