For what its worth, I've got both the 50 f/1.8 and 40 f/2.8. Although sharpness is similar, the 40mm is a much nicer and quieter lens to use. It would be my pick if I had to choose between them. (Although...the 50mm is a little longer and a nice portrait length on a crop camera).
With the cameras, I'd probably just buy the new t3i given the smallish price difference.