I just posted this on the DVXUser.com HVX200 forum as well. I'm surprised no one reported testing this before. If I did something wrong let me know.

I just did an interview job on a DVX 100A today and brought along my HVX200 just to get a nice comparison in a typical interview lighting situation.
We had talent in front of a dark grey textured backdrop with a broken up purple gel pattern. We were shooting 4:3 24P in ordinary miniDV tape mode so this should be an apples & apples comparison. (I am not sure if we had the same fstops or shutter speeds as I just wanted to get the same exposure quickly and I don't think that wouuld affect anything.)

First the HVX & DVX on identical scene file setups (SD Normal in this case) in 3200K preset - the color match was virtually identical. I only had to raise the HVX +1 point on color sat.

The noise issue though is what blew me away. The HVX200 was way cleaner than the DVX100A. Made it appear sharper as well though I wouldn't want to claim that.

The HVX @ +6 gain was cleaner than the DVX @ 0.
(All the detail settings were at 0 in both cameras.)

I was expecting the opposite. I do understand that the HVX100B is considerably cleaner than the 100A, but the 100A is what we have all gotten used to as a standard for miniDV.
This suggests that even if you have to push the HVX in low light its not going to be worse than the DVX100A.

Its going to make me sleep alot better tonight.

Now to be honest I briefly compared these two camera in a bright garage awash in mixed light and didn't notice this difference, so I would be interested in anyone else having a different experience.

BTW this was being viewed on a typical 8" Sony 8045 through the video composite outputs of both cameras.

I'll be doing this test also this weekend! i'll post my results later. But these are reasuring news, Leonard!

The noise issue though is what blew me away. The HVX200 was way cleaner than the DVX100A. Made it appear sharper as well though I wouldn't want to claim that.

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BTW this was being viewed on a typical 8" Sony 8045 through the video composite outputs of both cameras.

If you can see any noise on that sized monitor fed a composite signal then that's serious noise. The composite connection limits chroma bandwidth and 8" monitors are fairly low res.
Also the HVX200 is a HiDef camera, the aim is to be able to deliver an image that'll fill a cinema screen without looking shabby from the front row. Hopefully it can but an 8" monitor is no way to tell.

I'm not trying to say anything about how noisy this is as a Hi Def camera, compared to any other Hi Def camera.
However, with all the talk about how noisy the HVX may or may not be as a 1/3" chip camera I thought it was instructive to note that it substantially outperformed the DVX100A.
I personally was quite concerned and expected the opposite result since I knew that in 4:3 the HVX would only be sampling the center of that tiny chip in the first place. I also am using and expect to use it as a DV camera as well as an HD camera. Its good to know that even though it is slower than a DVX100A it will probably perform as well in low light with added gain.
I shot a feature with the original DVX100 and saw that blown up in theatres and never found grain to be an issue, so again this comparison was quite heartening to me.

Matches my experience too. I found the HVX to have an equivalent noise level to the DVX100B, and the 100B was noticeably lower in noise than the 100A.