Do you need f2.8 and are happy carrying the extra weight?
Yep, I'd say look at your pictures right now. Are a lot of them shot at f/2.8? Or, are a lot of them shot at lower shutter speeds (where IS would help)? Do you need to freeze subjects a lot (f/2.8 means faster shutter speed)? And, do you shoot a lot of the pictures at one end or the other (70mm, 200mm, etc)?
Just going from the T2i to a FF body will improve your light handling, so you might not need f/2.8 as much. Going to FF you'll lose some of the reach of the lens, but, also gain some on the wide end. If you use it at 70-135 a lot, you'll like that, if you use it at 200mm a lot, you might find you want more reach. In that case, there'd be some other things to consider.