I haven't done anything particular tbh.
I used Rebel's theme for IBrowse, and I converted any picture from Toolbar, status bar along with the main IBrowse html page (with the logo) to 8 colors using ImageStudio.
That trick helped a bit the loading times for IBrowse itself.
For websites, I dunno if it loads faster than other setups but I guess it doesn't.
My CPU is 030@36MHz (overclocked a bit the ACA630) and I'm using MANY new modules built into the custom ROM that I guess they can improve performance as well.
CF with new scsi.device is reaching 2.5MB/s so I guess that helps also.