Well that was the thing the XR520V is auto gain, you can not change it. In all the reviews, test and comparisons that are on my vimeo channel. The Sony had major noise because there was no way to manually correct it. The Canon has far less noise even at the higher gains. A few of the folks had commented that it was kind of amazing that the Canon wasn't showing the noise that was expected.
But as I mentioned, for a new diver and new video person. The Sony would probably be the safer way to go. The Canon is more for people who are going to use more manual controls. In addition the new Sony image stabilization would probably be an added benefit for divers.
For me I have still decided to stick with the Canon HF-S10, as I do intend to do a lot of stuff topside. And feel the use of more manual controls, and easier manual controls out weights the low light performance. Another thing that I haven't mentioned, we still do not know what controls will be available with the new Gates housings. So things could still change, depending on what controls Gates and the other housing manufacturers decide to offer.
I would like to see what you guys thought about the comparisons on the HF-S!) Vimeo Channel.