7D is a different planet from Rebels and 5D2 for sports.
It will not work exceptionally out of the box, but spend a little time setting up the AiServo behaviour (shoot, change, shoot, change, shoot, change) and it really is superlative.
It has the same sensor as the 550D, I get good results at night so long as I use common sense. I keep my exposures long with in-camera darkfield NR, and the ISO's low.
At night your exposures are always going to be longer, and if you add ISO's your images are always going to be noisier.
So accept these basics, get a sturdy tripod, a cable release and have fun.
The 7D benefits from RAW shooting and sensible RAW conversion. JPEGS fine in good light. If you are shooting in low light then shoot RAW and post-process. I like 0 NR on Luma channel and about 75% NR on chroma channel. Some very slight unsharp masking helps too.
A lot of folk bash the 7D, but then a lot of folk think that by spending more money they automatically get better pictures. It's a typical upgrade camera. By that I mean, the pros use 1 series and always have and always will.
I would guess that a sizable proportion of 7D sales are to former x0D and rebel class users, and the 7D is a camera that you just cannot approach with a x0D or rebel head on. Rebels are really designed to make life easy. the 7D needs a more considered approach.
None of this is to put you off, I don't want to come accross as in anyway patronising, just that you will read some bad press on the 7D, it's not my experience at all, but I knew what I was getting into.
If anything the 7D makes life more difficult, but if you work with it then it also makes much better pictures.
