I finally managed to get a paper turbine to turn with version 6. Instead of using a solar tower, I decided to keep the overall temperatures in the solar energy to heat conversion area lower to make construction more feasible. To that end I built a mini screen solar air heater and put it further from the fresnel lens' focal point (see the diagram below.)
To keep the solar air heater at the proper location at all times, I mounted it to the mirror of my fresnel lens and mirror solar cooker setup (see photos below.)
Testing with the paper turbine and PC fan
Test 1 - Paper turbine at hot air outlet
The paper turbine turned fairly rapidly at the hot air inlet as a result of the exiting hot air.
Test 2 - Paper turbine at cold air inlet
The paper turbine turned, but much more slowly, at the cold air outlet as a result of the entering cold air. This showed that the strength of the incoming cold air is less than that of the exiting hot air.
Tests 3 and 4 - PC fan at hot air outlet and cold air outlet
The PC fan did not turn at all at either the inlet or the outlet. I was able to turn it easily with my finger, so it wasn't being prevented by anything.
Construction of the mini screen solar air heater
Click on the photos for larger versions.
Video - Mini Solar Tower with Fresnel Lens Ver. 6 Screen Solar Air Heater
Here's a video I made of the setup, all testing and the construction.