Yes, it would be the best for you. As of right now. IF you ever wanted better, you could do the cable/hydro conversion and get a ITR tranny.
N2o wont run you a constant et. If you build the car for boost, you could run the ls tranny, stay under the boost range and have excellent gas mileage and when you needed constant, consistant power, you mash it, boom you hit boost.
You can full build the motor like a race motor, but it WILL eventually fail b/c of n2o. Now, Bill ran a 55 shot ZEX on his CX, 2 bottles of it without any problems, but i can garuntee you are going for more then a 55 shot.
You just need to build the motor YOUR way, if you are going NA, then yes, your tranny is the best, if you are going boost, then LS tranny. Running n2o doesn't make a matter in choosing a tanny.