If you read the specs, you will no doubt be impressed with the low light capabilities of the Rebel T2i -- ISO 100-6400 and expandable to ISO 12800 if needed. How does it perform in real life use?
I have said it too many times, the T2i has way too many pixels. As a consequence, it suffers in the low light performance department. The noise reduction system works pretty well removing noise and the jpegs are quite clean, but details are lacking at ISO 800 or higher. Comparing ISO 1600 with the 5D, I prefer the 5D output. The T2i files show much more artifacts and look muddy. The 5D files are cleaner. This sounds wrong, considering that the T2i goes all the way to ISO 12800, and the 5D only goes to ISO 3200. But to me, I wouldn't use the T2i above ISO 800, but I would happily use ISO 1600 or even the 3200 on the 5D.
The high pixel count does have one advantage -- resize the files by half makes them look much better.
BMW Dealership building -- T2i & 50mm f1.2L @ f2.2, ISO 800. Larger Picture.
The Red Rocket at the end of King Street. T2i & 50mm f1.2L @ f2.2.
Ryan -- T2i & EF 50mm f1.2L. ISO 3200. Larger Picture.