I tested both and honestly from what i hear on my Studio Sennheiser Headphones there is no difference audible. Despite the fact that double buffer has ultra unstable CPU spikes.
And i have fine ears according to my ear drum doc. I hear quiter tones on my right ear compared to the average human. That means i should hear a difference on the brass, cello, and Contrabass but i hear non. When i tested the Double buffer for the first time i thought i hear more samples and a better result but it turned out that this was just my brain tricking me because of the expectations to hear more.
I also tested between NP5 and stock Dorico Bbc Pro instruments on legatos and their is no audible difference with one exception. Noteperformer is quiter and smoother in the Transitions of legatos. All transitions are more gradual not harsh like on tradional midi playback with bbc pro