When I expose a wide brightness range scene (textured whites and deep shadows in midday sun) as far to the right as possible before the brightest tones clip (based on the RAW histogram), I see no banding. When I progressively underexpose the same scene, at some point I begin to see banding in low to middle tones sufficient to make the exposure unusable.
With a SONY HDSC I 94MB/s card, that point is two stops down. With a SanDisk SDHC I 95MB/s card, that point is three stops down. This is a result that surprises me and I can't explain it, but I can easily reproduce it. Based on this observation I won’t be using SONY cards, but I wonder if other cards might do even better. Leica says little on the subject: “Storage media: SD cards up to 2 GB, SDHC cards up to 32 GB.”
Does anyone know, based on actual experience, which cards are best in this respect?