Just a couple suggestions.
The 160GB drive is slower mostly because it uses platters that have less data density, meaning not as many bits are packed into the same area. So the platter has to physically move further along to retrieve the same amount of information as a newer drive with more data packed into the same area.
While the 500GB drives are smaller then the 1TB you have, it depends on if you have the newer version (WD5003AZEX) which is a gimped 1TB platter or the older version (WD5002AALX) which uses a 500GB platter. So you would have to know the actual makeup of how many platters and how big each platter is to understand how fast it should be. But "generally" a bigger drive will be faster then a smaller drive, especially if they are separated by a couple years or more, mostly due to the newer drive having denser platters.
Now the other thing that affects speed on a platter drive is the location on the platter where the test is done. A platter is a spinning circle, and you have to remember that the further out you move on a circle, the more distance you will cover on the circle for a given "speed" (RPM) of the platter.
So if your drives already have some data on them, when you go to use your benchmark, it is going to write and read to an unused area of the drive. Platter drives always start filling from the outside edge and move in. This means if the drive already had a considerable amount of data on it, then the benchmark will occur further in on the platter, which means you will get considerably less speed. From outer edge to inner edge, you can see a hard drives bandwidth drop in half. There's nothing that can be done about this, and it's one of the strengths of an SSD.
I would think that the raw speed would still be plenty for reading and writing song files. The access speed of the platter drives would be more a problem for seeking through the song (if it always reads from disk). For music...assuming not HUGE master files, I would always recommend using an SSD, again if space permits. For video, unfortunately due to the raw capacity needed you are almost always stuck using platter drives.
But again, it's up to you and your application. If you do not need anymore speed, do not worry about. And if you are having stuttering problems, that is more related to the access times which nothing will fix on a platter. RAID 0 will not affect access times. Only a faster spindle speed (10K or 15K RPM) or moving to SSD. If you are having problems where you are making small edits to the song file, that is not related to the transfer speeds you benchmark is showing. That is related to your hard drives ability to go in and change "random" areas of data on the platter. This is called the "4K Random" benchmark and is the Achilles heal of all platter drives because they HATE moving from one part of the platter to the other. Spindle speed can help a tiny bit, but the only true cure for random access speeds is moving to SSD. The absolute fastest platter drive in the world, is slower in 4K Random benchmarks then the cheapest, crappiest SSD's from 4 years ago.
4K Random is really the meat and potatoes of a hard drives ability. You have two extremes on a hard drives speed. Sequential and Random. One will be the fastest a drive can function at and one will be the slowest. Real world usage is much closer to the Random, then it is to the Sequential, unless you use the drive specifically to transfer large files such as video. Even pictures and compressed songs that are 5-10MB in size do not fully reflect sequential because the drive writes them too fast and has to move around. To see sequential you really have to be reading or writing a couple 100MB or more.
