Yes, do let us know the results!
I have just had another thought about my results. What I am trying to do is to reduce (ideally eliminate) the temperature difference between floor and ceiling, so that is what I should measure. With that in mind I took figures from the "no fans" and "both fans" data, and calculated that floor-to-ceiling temperature difference. I considered only ceiling temperature between 16 and 20 Celsius because that is where I have data for both series. Plotting the results and adding trend lines gives this graph:
This is a lot more promising. It shows that with both fans running the difference between floor and ceiling temperatures is consistently over 1 degree less than with no fans running. It was also nice to see that the 2 trend lines are parallel, which gives me a bit more confidence in the result.