If you are shooting raw, they also take a significant time to save. There's no way around that, it's a lot of data. The "busy" screen is also shown when dark frame subtraction is done, which essentially doubles the exposure time. Are you taking long exposures, or forcing this option on ?
CHDK can't make the camera shoot faster than the built in continuous mode, as this is mainly limited by the speed of the hardware. For fast shooting
- Get the fastest card you can
- shoot at the lowest resolution you can accept
- keep the ISO low, because the cameras do more noise reduction on higher ISOs
- disable raw if you don't need it
- disable dark frame subtraction (or shoot at exposure times that don't trigger it) if you don't need it
For resolution and ISO, you should test how your specific camera behaves.
