His conclusion: The T2i is clean up to ISO 800, and "useable" up to 3200.
He also compared it to the 7D and says the "T2i is definitely a step down in video quality," and adds "the T2i’s overheating issues alone makes it a no-go for me." Which is news to me. I hadn't heard of people complaining about the T2i overheating.
Finally, Jared Abrams at Cinema5D helped Hunter out with the test, and his writeup added an interesting detail:
It is also worth noting that we bumped up all the footage to Apple Pro Res and it showed very similar results as directly from the camera. The noise in Pro Res was much worse at ISO 1600 and ISO 3200.
Hunter Kerhart: T2i Lowlight Capabilities