Would a T5 tranny for a 5.0 be a practical application for a turbo 2.3L? Finding a 2.3 T5 is just about impossible for me, and I can buy a brand new 5.0 T5 from Ford Racing to go with a brand new 2.3L Turbo motor.
If you bought a new one and could get the one with the .8 (I think it is) overdrive, you might be alright.
A regular 5.0 T5 has a .6-something fifth gear, which just doesn't really work behind a 2.3 turbo (doesn't have the torque for that low of an overdrive)
The 5.0 T5 is probably going to have a 2.95:1 first gear, while the 2.3 T5 will almost always have a 3.97:1 first gear. Unless you've got a warmed up 2.3 making substantially more low end torque that stock, that 5.0 T5 is going to suck the life out of that car off the line.