Most things should be within the same ballpark. The trouble is at the moment that CSS polyfills are an order of magnitude (or two) off native performance. Examp

Most things should be within the same ballpark. The trouble is at the moment that CSS polyfills are an order of magnitude (or two) off native performance. Example: Current CSS layout polyfills (like grid, regions etc) suffer from this. Where you will see performance improvements is when developers create more expressive layouts/paints/etc. For example you can implement a grid layout with a bunch of nested flexboxes. You could also do it with the CSS Layout API. Because by using the CSS Layout API requires fewer divs, and maybe no N^2 layout passes, chances are it'll be faster. But this really gets at the point of Houdini is to inform browsers/specs what is important. If a grid/masonary polyfill becomes widely used, then it will help inform CSS work.