This is a comparison of the processing time for a page with 611 equations.
See the full page rendered with SVGMath, for lightning-fast processing.
See also SVGMath Overview for how it's done.
For each video, I did a "hard refresh" (Ctrl-F5) so all the page assets were loaded from scratch.
In the MathJax case, I first did a video of the original Stackexchange Math page. In that case, processing of the LaTeX finished in around 4 seconds (with text jumping around), but it took until 17 seconds for the rest of the page, plus scripts plus fonts to arrive. But that page uses version 2.7.1 of MathJax. In the above rendering, I'm using version 3.1, and it is only just marginally slower than KaTeX, and the rendering process is much smoother.
SVGMath is the fastest since it doesn't use any javascript processing on page load, nor does it need to wait for fonts to load (which is the case for both KaTeX and MathJax).