Depends on the operator and chemistry used. It would be very difficult to choose unless procedures and products were clearly defined. Even then, it would be a close call.
My gut feeling is that for the same carpet on the same day, with detergents and minimal agitation, the Powerflite would be No.1 If you were detergent free, with good mechanical agitation and cold water, the Scorpion would win.
Add heat to the Scorpion and it may just about be an all round winner, but both are excellent machines.
When I was considering what to buy myself a couple of years ago, I narrowed it down to just these two machines. I was happy using just hot water from the custy's tap or even cold. I concluded that if I chose the Powerflite, I'd still want more power, so I bought the Scorp. It's only natural to want to use the biggest tool in the box. For me it was the right decision.
Safe and happy cleaning

Ken