Org Mode and Observable are both performant enough. Unfortunately, they have their own limitation. In Emacs+Org Mode, you're working with a rich text display as a canvas, so while you can output images easily, forget about interactive GUI (charts, control sliders, what not) - at least without some dark hacking magic.

Observable - that's a true joy if you want fast feedback and interactivity. It's as fast as your browser, since your notebook is entirely client-side executed JavaScript. It's an order of magnitude better option than regular notebooks if you want to do some exploratory or scientific visualization. It's main drawback: JavaScript. That's what you're limited to. So forget about your favorite Python or R libraries (at least without dark hacking magic).

Observable did not handle my rendering requirements involving several hundreds of data points for my parallel coordinate plot. That said I'm not sure how it would fare outside of the notebook setting.

It should be as fast as equivalent visualization done in the frontend of a web page; after all, what you do in Observable gets directly executed by your browser. I wonder what your particular requirements are. On my end, I had acceptable performance on interactive prototypes involving updating multiple histograms, where inputs had tens of thousands of points.