I would call Speckled Roman sweet and Joe's Plum more tangy & complex, like a good slicer/beefsteak tastes. Uncle Steve's I don't remember, but that pic, the pile is maybe 6-8" high on that plate, which is 9 inches diameter.
I hate giving taste descriptions because everybody has different taste perceptions but I use smell as a very important factor in taste.... the ones I talked about aroma "reek" great taste.
Rio Grande is a determinate that usually topples those 3-ring cages--you need a good stake too. You'll get about 4 quarts per plant.
I can't describe the taste cooked because when I make sauce, I use all the varieties mixed in... but I heard from others the Ernie's Plump makes one of the richest sauces.
And here's Sarnowski Polish Plum:
...and Wuhib:
...and Heidi:
For an orange sauce try these:
Roughwood Golden Plum (Yellow Brandywine x San Marzano):
...and Orange Banana: "INDETERMINATE. Orange Banana was the clear winner of an autumn paste taste at the Shipmans in Maine. Sweet flavor of Sungold but with more depth, makes a great sauce by itself, or adds a fruity complexity to other sauces. Orange fruits 3-4" long avg 4-5 oz."
Throw in some Herman's Yellow, a great tasting heart with few seeds:
...or brighten it up a bit with Power's Heirloom:
