Minor differences in the TY757Vxxxx transmissions are usually gear ratios, differential ratios (also known as final drive ratio), and Synchronizer rings.
I can attest to the TY757VBCAB being a pretty bad transmission. (mine started making noises at 150k miles). I currently have a TY757VBABB out of a JDM '04 2.0gt Spec.B in my '05 2.5i. Wonderful transmission, and I got it for really, really, cheap. The catch is I had to replace the rear differential (in this case a 4.44 VLSD off of an '04 Forester XT).
I have also *had* a TY757BBAB out of a JDM '05 2.0gt which was making bearing noises (Or so I thougt... truthfully I think it was low on fluid). When I swapped this trans in to my 2.5i, I also replaced the rear diff with a 4.11 VLSD.
The transmissions will bolt right up as expected, but I do have some notes specific to the TY757Vxxxx's that you may find helpful.
1. The Turbo cars and the N/A cars use different Reverse/Neutral Sensor harnesses, in order to make the swap work, you will need to pull the harness off of your original trans and out it onto the new one. (Sensors are the same though)
2. Make absolutely sure that both sensors have a washer on them when inserting them. Without a washer the neutral sensor makes contact with the shift rail internally causing the gear shift to bind. In my case the gear shifter was very hard to move, and I could only get the car into 1st,3rd, and 5th gear and even then it did not feel like it was actually in gear.
3. Replace the axle seals on the transmission before you put it into the car.
4. The dipsticks between the turbo trans and the N/A trans are different. Either will work on the N/A.
5. When shopping for clutches, note that the clutch fork in the turbo trans may be different than the throw out bearing coming with a clutch kit is designed for. The Clutch fork the on TY757VCACA is thin and narrow, and the TOB won't fit on the Turbo trans fork. This may take some guessing, but as far as I can tell the TY757VBBAB had a newer style thicker/wider fork and the TY757VBABB had a smaller thinner fork. The TY757VCACA's TOB almost looks like it would fit on the TY757CBABB's fork, but it doesn't.
6. The 05-09 Legacy's do not have speed sensors on the trans.
7. Drain the trans fluid before you drop the trans, and don't fill it until it's back in the car. (It will spill out when full, and either the driveshaft or axles aren't inserted.)
Hope this helps!