I mean all independant trials of course

I think those two are the only independent ones, I quite regularly try to follow (scientific) literature on peonies and those are the only ones I know of that have compared many cultivars. The RHS study may be the most interesting one as it is more recent and thus also compares newer cultivars. The Dendroflora one is somewhat biased towards the most widely grown ones in my opinion. For example giving both Sarah Bernhardt and Mme Claude Tain the maximum of a three star review seems over the top for me. In the description for each cultivar it is mentioned that both have sturdy stems, which is utter nonsense of course. Both are healthy and give lots of stems each year which makes them good cut flowers, but both will also tend to flop when it rains. Otherwise a perfectly healthy, vigorous and upright cultivar like Do Tell is placed in the category ‘can be discarded’.

The peonies listed in the ‘Award of Landscape Merit’ of the American Peony Society is a better list to go by I think. At least compared to the Dendroflora article. The RHS study is better I think, although I have only browsed it superficially.

There are a few show gardens where you can see thousands of cultivars and compare them side by side. Unfortunately the two larger ones I know in the Netherlands (Greenworks and R2) are both only accessible for professional growers. They would be good places to make an honest assessment as they both have recent introductions. And given the -IMHO- excessive numbers of new introductions it would be nice to have that.