@reyalp
The Super-fine mode provides a noticable improvement. It reduces the JPEG artifacts on the SX200 almost to the level of the noise at low ISOs. There's still a little smearing that I was hoping a 'super-super-fine' or 'no compression' mode would eliminate. Then shooting at, say, 1600x1200 (2MP) would provide a 2MB filesize while allowing zooming to 30x without resorting to 'digital' zoom, thus preserving IQ as much as possible. Given the zoom lens, I prefer to do my framing/composing/cropping/enlarging in-camera, and not do any post-processing or RAW-JPEG conversion later on. I'm thinking that a no-compression mode would still allow the camera to do the white balance, custom color adjustments, etc., but just wouldn't 'compress' the file. I guess it would be equivalent to the camera doing the RAW processing, with the camera setting the WB and color adjustments, and with a resulting JPEG filesize of whatever the MP setting is.
Of course, this assumes that CHDK would have any way of controlling the actual compression level...