According to my definitions and experience
The Canon XL2 and Panasonic AG-DVX100 are in the "professional" camcorder camp. Compared to consumer-grade camcorders, they have big lenses, big imaging chips and use XLR audio in connectors. They are both standard definition camcorders - they can do DV (4:3) and DV widescreen (16:9) - but they are standard def only.
The Sony HVR-HD1000 is a lot less money, and is essentially just a higher end consumer cam housed in a shoulder-mount form factor. As I recall, the lens (43mm) and single CMOS imaging chip are the same as those used by the HDR-HC1 (and HVR-A1U) and it has only a stereo 1/8" (3.5mm) audio in jack. While it may be part of the "pro" Sony line up, it does not quality (under my personal criteria (though I have every confidence few consumers would buy it - but some professionals might). Personally, I think the HDR-FX7 is a much more robust camcorder - and it falls into the prosumer category (it's pro sibling, the HVR-V1U, has XLR audio inputs).
The key to your requirement is getting the largest lenses and imaging chips you can afford (to cover for the low light environments). I think you are on the right track with the XL2 and DVX-100, but if you want to jump into high definition, the prosumer Sony HDR-FX1000 (its pro sibling was the HVR-Z1 - and now is the HVR-Z5) is worth investigating - and comparing to the Canon XHA1. The Panasonic "entry" would be the AG-HVX200 and is probably outside your budget (and it uses fairly pricey "P2 cards" for high definition DVCPRO HD video capture storage). The JVC GY-HM100 is worth a look, too.