PP is short for the computers parallel port.
8% is not that bad, well kind of......
My punny Sherlne will drop 4 to 10% and have no problem getting a good thread. I have tested where the spindle was even stopped for a split second and the threading cycle recovered. If memory serves me correctly, you can go down some 20 to 30% and the threading cycle will recovery from it.
The goal should be very little drop in rpm ( actually its motor torque / power that we are really talking about).
You should play with your small lathe trying different speeds and feeds and see what works for different materials and cut depths, make note of them. Ideally you want no drop in the rpm. Try increasing the spindle speed and use shallower cuts. Aslo you can try a different angle, like 15 degrees instead of 29 or 30 and flank cut the thread.
So, you should be looking to reduce the rpm slow down as much as possible.
RICH