My idea, and I'm not working on this is at the moment, so don't ask...
To get an idea of how fast netsurf or OWB or whatever browser could be on slow machines one could port it so it just writes to a fast-mem buffer without displaying anything, except a "loading... block in window area" and see how that times out, then work on how to transfer the buffer data to Amiga window rastport depending on how it's updated and what screen type it has to render to. Maybe draw some best match luma levels first then add best match chroma info for some fixed pallette pens, etc. for low color screens such as a 16color workbench, or even open its own 8bit greyscale only screen and use that. It might not be pretty, but might be usable... Then go on to investigate profiling the underlying HTML, etc. and layout engines in more depth, options for javascript, plugins, etc.