A new Card (SanDisk Extreme SDHC 32GB UHS-I) gives me more than 52Mbyte writing with RAW Data.
Measured without CHDK gives nearly same results.
Plotted is the difference of the timestamps in the RAW data (which is more accurate than 1s). Once with 64GB Samsung EVO Plus and with SanDisk Extreme SDHC 32GB UHS-I. RAW File size around 24MByte