Computurd,

The only application I can think of that lets you set QD is iometer

User selectable QD in normal applications is not possible, like One_Hertz says, it requires different "coding" and many applications would not benefit from this.
(due to the nature of how applications process the data)

On top of this, SSD's have changed the picture a bit, using HDD's the "CPU" was more likely to wait for the HDD than the other way around.
Today it is more likely that the "SSD" is waiting for the "CPU" to process the data.

note:
For an application to send "disk" commands in parallel it needs to be coded differently (multi threaded).
The only other possibility is that multiple applications run i parallel.
(of course it can be a combination of the two)