My first thought is to try it with both on. Any ideas would be appreciated.
Both QDEO and Reon are good scaling solutions. You should get good results no matter which you decide to use.
You cannot turn off the processor. This is because of many things. If you use keystone, guess what you are using, the video processor. Depending on the machine when you adjust the brightness or contrast that to can be the video processor, etc etc.
"You buy a Ferrari when you want to be somebody. You buy a Lamborghini when you are somebody." - Frank Sinatra
Even when you feed the display 1080p, you might still need the vp to do colour space conversion, chroma upsampling, frame rate duplication (for 24p) and of course the usual picture adjustments. There might also be background non-defeatable video processing going on and some degree of overscan unless there is a way to disable that.
Audiosceptics accept audio trials using 25 people. A recent Oxford study with over 353,000 patient records from 639 separate clinical trials shows for every 1,000 people taking diclofenac or ibuprofen there would be 3 additional heart attacks, 4 more cases of heart failure and 1 death every year.