The people from the german CHDK-forum gave me a link to this "HDR-Script": http://www.wirklemms.de/chdk/forum/viewtopic.php?p=4695#4695. I've tested it and it works quite fast if you shoot in JPG and with fixed focus (You can fix the focus manually before the shooting). Maybe you want to have a look on this to implement it in your script?
You can preset the focus on my script, or have it prefocus itself on the first shot and lock it in.
The big advantage in the way I set mine up is that you can set the bottom and top exposure levels 'live'.
- Start the script (best in manual mode, but Tv will work too).
- From the adjust menu, select the start exposure, the script will pause and you can close the <alt> menu and manually adjust your shutter speed unitl you see the exposure level you want to start with, then restart the <alt> menu. When a button is pressed to resume the script, it reads the selected shutter speed and sets the start exposure to it. You can then do the same with the end exposure.
- You can then set how many shots or steps you want to iterate through from start to end
This takes some of the guesswork out of determining the appropriate exposure range and step values. Once, the shootiong has started, it should be as fast as the one you linked (unless prefocus and manual focus is off).