The t4i shoots up to 6400 iso. It appears with a side job I just landed this morning, the 70-200 2.8 non IS will be in reach.
Actually, it goes up to ISO 12800, with ISO 25600 available as an expanded setting (H). But whether ISO 6400 is actually usable
, much less ISO 12800 or higher, is another matter. Just because the setting is available, doesn't mean you should use it - the 1D X has ISO 204800 available, but it's not even remotely usable.
Reportedly, the T4i actually a little noisier than the predecessor sensor (the one in the 7D, 60D, T2i, T3i). That's probably artificial due to some tuning by Canon, since it's sharper than the predecessor sensor, too (noise can be traded for sharpness, and vice versa). Personally, I find ISO 3200 on the 7D to be usable, but only just, and I really prefer to keep the ISO around 800. But, noise tolerance is subjective, so if you're happy with ISO 6400 on the T4i, great!