A t2i is extremely capable. That's what I have. The FF I used was borrowed.
I'm going to move to FF though when I can justify the money.
Canon are faggots though because the new t5i offers no real world benefit over a t2i. They added bells and whistles, but at the end of the day it still has the same 18mp sensor. And since I shoot in manual 99.9% of the time, all that other crap adds me no benefit. A t2i right now is a serious bargain buying one lightly used.
I have my eyes on the 6D because it offers better IQ than the 5D3, though it's neglible, but the price is far apart. What you lose out on is a world class AF system that the 5D3 has, but it's not with paying $1500 for it. I'm most concerned with sharpness, detail, dynamic range and accuracy of color. The FF does these much better than a crop.