When I was doing my filler loads,, using Bullseye & all, it was back in the late 1970's & into the early 1980's. It was when I was on a budget,, and I wanted Bullseye to be a "do all" powder w/o costing me much. Well, as time passed & I found I really needed to find the best powder/bullet combo & not try & be so frugal,, I stopped loading that particular load.
I had studied a lot about fillers back then,, including the use of cream of wheat etc. In my mind,, using anything that would mix with the powder didn't feel right in my opinion. And back then, I didn't have a Chrono, or anything else to help me study the differences,, so no,, I do not recall any stand out revelations about filler vs. non-filler loads.
But I do know that later on,, when I did get my Chrono, I found that my old loads were quite good in Extreme Spread & Standard Deviation. Plus,, quite accurate too!