@rds Thank you for your in dept explanation on how you plot drives.

Yes the main slowdown is writing to disk. I get 8000 nonce's/min speed when the drive is written 20% for one "thread" the CPU is done whit the calculation then the fond turns gray and the CPU has to wait for the writing to stop. So yes I have the same problem as you the disk write speed is to low....
Also for the first three thread it writs weary fast then the speed drops down....