Thanks Mike and Dennis.
Dennis - yes, this was taken with the FS102, onto an unmodded 350D via the G11 guided with the FS60-C. I guess that the HDR process used the 10x15-sec subs to truly average out the 4x360-sec exposures. In any case, most of the magic was seen right after the HDR combination was performed, the white point set and then gamma on conversion to 8-bit.