But back to the original posters question, if a prosumer camcorder/housing rig is in your budget go for it. But if its a decision between a consumer SD camcorder and a consumer HD camcorder, I would go with the HD.
I second this comment too. While the Sony 3 CCD cameras are quite versatile, the HD cameras blow them away. IMO their time UW SD has come and gone. I recently shot some footage on a 1 CMOS camera in pretty dark water (with 100 watts of HID behind it) and came out better than expected. Vibrant, lush and there is nothing like 1080 on a big HD LCD tv.
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