To the OP: The only thing I recommend, if you plan thing a 7D might fit your needs, is to rent one and try it out in lower light situations. The 7D is one of those cameras you either love or you hate. I recommended it, like everyone else here, to someone about a year ago, and they absolutely hated it. I think their hate was unwarranted, and their complaints rather exaggerated the facts, but still...its a love or hate camera.
The problem is, while it was an EXCELLENT camera for it's time, it did not utilize a process shrink to the new 180nm process that more advanced sensor designs were starting to use at the time. Its 18mp sensor, the ubiquitous Canon 18mp sensor, is still manufactured on the decade-old 500nm process. As such, it lacks the photodiode area to support a decent FWC (it's only 20k e-), which limits the maximum potential SNR, which has a direct impact on noise. Even at ISO 100, the noise performance at 100% crop (or in other words, assuming you intend to utilize all of the pixels the 7D has to offer), is marginally better than the 5D III at ISO 400. ISO performance above 1600 is fairly poor as well as an additional amplifier is used for 3200 and 6400, and while with work you can get some usable shots at ISO 3200, images can still be quite noisy at that level.
If you are the type of person who
cares very much about noise performance, then I really do highly recommend you rent the 7D first and try it out in the most demanding situations you think you'll use it in. Anyone who has used the 5D II in the past, or other FF cameras with their nice, big pixels and gargantuan full well capacities, will probably have issues with the noise of a 7D. Additionally, the 7D was the first generation of products to use the Canon 18mp APS-C sensor, and is also the only product to use dual DIGIC chips to process the images (which can cause quite intrusive vertical banding right into the mid-tones if you fail to maximize SNR with ETTR.) Canon's handling of that sensor improved with later generation Rebel products, and I've read, heard, and chatted about too many cases where people have found the 550D and 650D produced slightly better IQ than the 7D.
The AF system and frame rate are the real selling points of the 7D. If you need them and can't afford a 1D body, then there really isn't any other camera that fills the role the 7D does. If you can live with the noise, don't need ISO's above 1600 very often, and care more about locking focus, tracking your subjects, and getting the shot with lenses that cost less than $5000...then it is the camera for you. Just make sure you can live with the noise!