Got a new system about a year ago. Pretty good spces: i7 3570k, 16gb ram. Have a dual boot system: windows on an ssd, linux mint on a normal hdd.
While both are fast...windows on ssd is crazy fast. The only thing holding me back from switching linux to an ssd is that I'll probably have to reinstall and reconfigure it, and I just haven't had the wherewithall to do that yet.
Bottom line: 90 percent of the time, on a powerful system with a normal hdd, your bottleneck is the hdd. Raid makes almost no difference compared to ssd because the limitation of hdd's isn't the overall transfer rate, but how quick the hdd can seek to different areas of the drive. This comes in to play when you boot up a program, and it has to load a bunch of different files. SSD's are literally magnitudes faster at this, which is why, for me, chrome with 100 tabs takes about 20 seconds on linux mint, and about 1/2 a second on windows.