There's a great explanation of read striping here:
http://blog.covecube.com/2013/05/stablebit-drivepool-2-0-0-256-beta-performance-ui/
As described in the forum post, in general, with x4 duplication you are not going to get a x4 boost in performance. There may be some boost depending on how that particular application is reading data (asynchronous reads are best), but generally read striping prevents stuttering due to lag on spinning drives.
From the above blog post:
Now, let’s say some process starts on disk I:\, something that completely saturates the disk. Normally at this point your media would start to stutter very badly. And because the media player is reading the data rather slowly, the standard bulk mode read striping algorithm would have no outstanding I/O to lock onto, in order to tell it to switch disks.
Well, here’s what the new system does in this case.
[screen]
As you can see, we’re still streaming at a very good 5.75 MB /s and more importantly, DrivePool has all but stopped reading from I:\ because it’s very busy. Your media keeps playing without stuttering and you would never know that anything happened at all.