Hey, I am in Titusville, just east of Orlando, and there is a yellow plum in my Mom's neighborhood. I have seen it fruit heavily for it's size, for at least the last 6 years. The tree is around 5 feet high and planted underneath a few oaks, and a sycamore. I am not up to speed on plums, but I am always impressed by the tree and yield. I will try to get the specs on it soon.
Andre